A composite cathode material, its preparation method and application

Abstract

This invention provides a composite cathode material, its preparation method, and its application, belonging to the field of cathode material preparation technology. The method includes: placing sodium sulfate and ferrous sulfate heptahydrate in a reaction vessel and performing a primary sintering under a protective atmosphere to obtain an intrinsic sodium ferric sulfate material; introducing a mixture of carbon source and carrier gas into the reaction vessel, coating the intrinsic sodium ferric sulfate material with conductive carbon material using chemical vapor deposition, and performing a secondary sintering to obtain the composite cathode material. This invention achieves a one-step coating process of conductive carbon material after sintering of the sodium ferric sulfate composite material via chemical vapor deposition, realizing the preparation of the composite cathode material in one step. This greatly simplifies the cumbersome steps in step-by-step coating and synthesis methods, reduces battery production costs, achieves uniform dispersion of carbon material in the sodium ferric sulfate cathode material, and improves the electrochemical performance of the composite cathode material.

Description

Technical Field

[0001] This invention relates to the field of cathode material preparation technology, and more specifically, to a composite cathode material, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid growth of the global population and the rapid development of the world economy, finding low-carbon, green, and renewable energy sources has become particularly important for addressing climate change, improving the energy structure, and developing a sustainable economy. Among these, representative new power generation methods such as solar, tidal, and wind power have attracted worldwide attention. However, these energy forms are severely constrained by natural conditions and geographical location, and their power generation stability and continuity cannot be guaranteed, preventing direct integration into the power grid. Therefore, finding systems for large-scale energy storage has become a critical issue that urgently needs to be addressed.

[0003] Chemical energy sources have garnered widespread attention due to their high energy density, efficiency, and good cycle stability. Among them, lithium-ion batteries, with their high energy density, fast charging capability, good cycle stability, and wide operating temperature range, are currently widely used in the electric vehicle industry. However, the limited lithium resources on Earth lead to prohibitively high production costs for lithium batteries. Therefore, finding alternative rechargeable battery materials is of paramount importance in chemical energy storage.

[0004] Sodium and lithium belong to the same main group in the periodic table, and both their physical and chemical properties make sodium a theoretically viable alternative to lithium-ion batteries. Furthermore, Earth's sodium resources are abundant, 400 times that of lithium, and are widely distributed. Refining them is also simple, resulting in relatively lower production costs for sodium-ion batteries. Therefore, sodium-ion batteries are widely considered a strong alternative to lithium-ion batteries due to their cost advantage.

[0005] The performance of sodium-ion batteries primarily depends on the electrochemical properties of the cathode material. Currently, the main cathode materials for sodium-ion batteries include layered oxides, polyanionic compounds, and Prussian blue compounds. Among these, polyanionic compounds have significant advantages in sodium-ion battery cathode materials due to their open framework structure, low-energy ion migration pathways, and adjustable voltage range. Polyanionic sodium iron sulfate cathode materials, in particular, have attracted widespread attention due to their lower production costs and higher operating voltages. However, these materials generally have poor conductivity, hindering the realization of their excellent energy storage properties. Furthermore, their susceptibility to water absorption and oxidation by atmospheric oxygen leads to material failure. To address the issues of water absorption and poor conductivity in cathode materials, modification is necessary. This is typically achieved by doping or coating with materials with good conductivity, such as carbon nanotubes, graphene, and carbon nanowires. Similarly, to address the drawbacks of water absorption and oxidation, anti-oxidation and anti-water-absorption materials can be added to achieve good electrochemical performance in the cathode material. In existing technologies, ferrous sulfate heptahydrate usually needs to be pre-dehydrated and ball milling is used to mix conductive carbon materials and sodium ferric sulfate composite materials. This process is complex and has high production costs. Furthermore, the synthesized intrinsic polyanionic sodium ferric sulfate cathode material has many problems such as low specific capacity, poor cycle stability, and unsatisfactory rate performance. Summary of the Invention

[0006] The problem solved by this invention is that existing intrinsic polyanionic sodium ferric sulfate cathode materials have at least one of the following problems in the synthesis process: complex production process, high production cost, low specific capacity, significant cycle decay, and unsatisfactory rate performance.

[0007] To address the above problems, this invention provides a method for preparing a composite cathode material, comprising:

[0008] Sodium sulfate and ferrous sulfate heptahydrate were placed in a reaction vessel and sintered once under a protective atmosphere to obtain intrinsic sodium ferric sulfate material.

[0009] A mixture of carbon source and carrier gas is introduced into the reaction vessel, and conductive carbon material is coated onto the intrinsic sodium ferric sulfate material using chemical vapor deposition, followed by secondary sintering to obtain a composite cathode material.

[0010] Preferably, the flow rate of the mixed gas is controlled at 0.1-0.5 L / min, the deposition temperature of the chemical vapor deposition is controlled at 300-500℃, and the deposition time is controlled at 0.1-10 h.

[0011] Preferably, the volume fraction of the carbon source in the mixed gas is controlled at 5-8%.

[0012] Preferably, the carbon source includes one of acetylene, methane, and acetone.

[0013] Preferably, the flow rate of the protective atmosphere is controlled at 1-10 L / min.

[0014] Preferably, the temperature of the first sintering is controlled at 300-500℃ and the time is controlled at 6-24h.

[0015] Preferably, the amount of sodium sulfate is x, the amount of ferrous sulfate heptahydrate is y, and the ratio of x to y satisfies the following relationship:

[0016] 0.1≤x / y≤4, 2≤x+2y≤100.

[0017] Preferably, the temperature of the secondary sintering is controlled at 300-500℃ and the time is controlled at 6-24h.

[0018] The advantages of the composite cathode material preparation method of the present invention compared with the prior art are as follows:

[0019] This invention achieves the preparation of composite cathode materials in one step by simultaneously performing the sintering of intrinsic sodium ferric sulfate material and the coating of conductive carbon within a reaction vessel. This greatly simplifies the cumbersome steps in stepwise coating and synthesis methods, reduces the time required, optimizes the synthesis process, and reduces battery production costs. Furthermore, the one-step coating of conductive carbon material after the sintering of the sodium ferric sulfate composite material is achieved through chemical vapor deposition, ensuring uniform dispersion of the carbon material within the sodium ferric sulfate cathode material and improving the electrochemical performance of the composite cathode material.

[0020] The present invention also provides a composite cathode material, which is prepared by the method described above.

[0021] This invention also provides an application of a composite cathode material as a cathode material for sodium-ion batteries.

[0022] The composite cathode material of the present invention and its application as a cathode material for sodium-ion batteries have the same advantages over existing technologies as the composite cathode material, and will not be repeated here. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the preparation method of the composite cathode material in this embodiment of the invention.

[0024] Figure 2 This is another flowchart illustrating the preparation method of the composite cathode material in this embodiment of the invention;

[0025] Figure 3 The image shows the XRD pattern of the composite cathode material synthesized in Example 1 of this invention.

[0026] Figure 4 The first two charge-discharge curves of the composite cathode material synthesized in Example 1 of this invention are shown in the voltage range of 2.0V-4.5V and the current density of 0.1C. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0028] like Figure 1 As shown, an embodiment of the present invention provides a method for preparing a composite cathode material, comprising:

[0029] Sodium sulfate and ferrous sulfate heptahydrate were placed in a reaction vessel and sintered once under a protective atmosphere to obtain intrinsic sodium ferric sulfate material.

[0030] A mixture of carbon source and carrier gas is introduced into the reaction vessel, and conductive carbon material is coated onto the intrinsic sodium ferric sulfate material using chemical vapor deposition, followed by secondary sintering to obtain a composite cathode material.

[0031] This embodiment directly mixes sodium sulfate and ferrous sulfate heptahydrate in a reaction vessel for a single sintering process. This eliminates the need to pre-remove the water of crystallization from the ferrous sulfate heptahydrate. Instead, the high temperature during the single sintering process converts the water of crystallization into water vapor, which is then carried out of the reaction vessel under a protective atmosphere. This eliminates the pre-treatment and dehydration process required in existing technologies, shortening the process flow and reducing costs. After sintering, a mixed gas is introduced into the reaction vessel, and conductive carbon material is deposited in one step onto the surface of the intrinsic sodium sulfate material obtained from the single sintering process using chemical vapor deposition. This yields a sodium sulfate composite material with well-uniform carbon coating size. A second sintering process further enhances the density of the coating layer and improves material properties, ultimately producing a sodium sulfate composite cathode material with uniformly coated conductive carbon.

[0032] This embodiment provides a one-step method for synthesizing sodium ferric sulfate cathode material in a reaction vessel. Using chemical vapor deposition (CVD), a conductive carbon material is deposited on the surface of the sodium ferric sulfate cathode material by introducing a carbon source gas into the reaction vessel. The "one-step" method refers to placing the reactants sodium sulfate and ferrous sulfate heptahydrate in the reaction vessel, and then adjusting the sintering temperature, time, and parameters of the introduced mixed gas to achieve the synthesis of the sodium ferric sulfate cathode material and the deposition of conductive carbon material on its surface. Compared to the existing two-step solid-phase method that requires dehydration of ferrous sulfate heptahydrate, sintering, and then mixing in conductive carbon material, this embodiment improves upon the solid-phase synthesis of sodium ferric sulfate composite cathode material by modifying the sintering process of sodium sulfate and ferrous sulfate heptahydrate and the coating process of conductive carbon material. By simultaneously performing the sintering of the intrinsic sodium ferric sulfate material and the coating process of conductive carbon within the reaction vessel, the composite cathode material is prepared in one step, greatly simplifying the cumbersome steps in the step-by-step coating and synthesis methods and reducing battery production costs. Furthermore, this embodiment utilizes chemical vapor deposition (CVD) to achieve uniform carbon deposition within the material, resulting in more uniform carbon dispersion within the sodium ferric sulfate cathode material. This suppresses instability during the cathode material synthesis process, further enhancing the material's cycle performance and resolving the issue of uniform carbon dispersion in conventional sodium ferric sulfate composites. Additionally, by directly depositing a mixture of sodium sulfate and ferrous sulfate heptahydrate into a carbon-source atmosphere in a reaction vessel, a one-step process is employed to form a carbon-coated sodium ferric sulfate composite. During this process, the carbon source gas flow rate, coating time, and coating layer thickness can be adjusted to create a uniform and dense conductive carbon coating layer. This improves the composite cathode material's susceptibility to water absorption, poor conductivity, and low rate capability, significantly enhancing its overall performance and specific capacity. Moreover, the CVD method is simple, easily industrialized, and reduces production costs, making it significant for the commercial application of this cathode material.

[0033] In some embodiments, the reaction vessel is a vacuum rotary tube furnace used for chemical vapor deposition. That is, sodium sulfate and ferrous sulfate heptahydrate are directly mixed and placed into the rotary tube furnace, where the sintering of the intrinsic sodium ferrous sulfate material and the coating of conductive carbon are carried out simultaneously. This saves costs and yields a sodium ferrous sulfate composite cathode material with more uniform coating, which plays a crucial role in improving the conductivity of the sodium ferrous sulfate cathode material and effectively utilizing its electrochemical performance.

[0034] In some embodiments, sodium sulfate and ferrous sulfate heptahydrate are placed in a vacuum rotary tube furnace for chemical vapor deposition in a specific molar ratio, and a protective atmosphere, such as argon, is introduced. The evaporated water vapor is then blown out by controlling the flow rate of the protective atmosphere. The amount of sodium sulfate is x, the amount of ferrous sulfate heptahydrate is y, and the ratio of x to y satisfies the following relationship:

[0035] 0.1≤x / y≤4, 2≤x+2y≤100.

[0036] The flow rate of the protective atmosphere is controlled at 1-10 L / min, while the temperature of the first sintering is controlled at 300-500℃ and the time is controlled at 6-24h.

[0037] In this embodiment, the dehydration of ferrous sulfate heptahydrate is carried out simultaneously with the reaction of sodium sulfate and ferrous sulfate heptahydrate. The temperature during the primary sintering reaction is used to evaporate the water of crystallization in the ferrous sulfate heptahydrate, producing water vapor. Then, by controlling the flow rate of the protective atmosphere, the protective gas carries away the water vapor, thus removing water from the material. It is understood that the flow rate of the protective gas has a significant impact on the effectiveness of the primary sintering reaction. If the flow rate is too low, the generated water vapor cannot be removed, affecting the normal progress of the reaction; if the flow rate is too high, it wastes gas and can also lead to uneven temperature distribution within the furnace, resulting in excessively low furnace temperatures. Therefore, in this embodiment, the flow rate of the protective atmosphere is controlled at 1-10 L / min. Within this flow rate range, water vapor can be blown out to achieve the dehydration of ferrous sulfate heptahydrate without affecting the reaction temperature of sodium sulfate and ferrous sulfate heptahydrate.

[0038] In this embodiment, when synthesizing sodium ferric sulfate cathode material, a vacuum rotary furnace is used to directly perform one-step carbon deposition coating of sodium sulfate and ferrous sulfate, eliminating the need to pre-remove the water of crystallization of ferrous sulfate heptahydrate. By controlling the inert gas flow rate during the sintering process in the vacuum rotary furnace, water vapor is blown out as the furnace gradually heats up. Compared with the prior art, which requires pre-dehydration treatment of ferrous sulfate heptahydrate, this embodiment simplifies the production process, reduces production costs, and is conducive to large-scale production.

[0039] In some embodiments, the sintering and deposition processes are carried out by controlling the sintering temperature, time, and type of inlet gas in a rotary tube furnace. During sintering, argon or similar gases are used as a protective gas. During carbon deposition, acetylene, methane, or acetone is used as the carbon source, and argon or similar gases are used as the carrier gas. A mixture of carbon source and argon is gradually introduced, and the flow rate of the mixed gas and the deposition time are controlled within a specific temperature range to perform chemical vapor deposition of conductive carbon materials. Specifically, the flow rate of the mixed gas is controlled at 0.1-0.5 L / min, the deposition temperature of the chemical vapor deposition is controlled at 300-500°C, and the deposition time is controlled at 0.1-10 h, thereby obtaining carbon coatings of different thicknesses.

[0040] In a preferred embodiment, the volume fraction of the carbon source in the mixed gas is controlled at 5-8%. By controlling the volume ratio of the carbon source in the mixed gas and the flow rate of the mixed gas, carbon coating layers of different deposition thicknesses can be obtained. The remainder of the mixed gas is a carrier gas, which is used to transport the carbon source gas. Inert gases such as argon are used as the carrier gas to ensure an oxygen-free environment during the carbon deposition process.

[0041] To improve the conductivity and electrochemical performance of intrinsic sodium ferric sulfate, this embodiment employs carbon coating to obtain a carbon-coated sodium ferric sulfate cathode material. During the carbon coating process, this embodiment leverages the uniformity advantage of chemical vapor deposition (CVD) technology. A carbon source gas is introduced during the sintering of the sodium ferric sulfate cathode material, and the coating thickness is controlled by adjusting the gas flow rate and coating time, resulting in a uniform and dense conductive carbon coating layer. Compared to the prior art of mixing conductive carbon material and sodium ferric sulfate composite material through ball milling, this embodiment achieves uniform dispersion of carbon material in the sodium ferric sulfate cathode material. Furthermore, since CVD and sintering can be performed in the same reaction vessel, only the carbon source gas needs to be introduced into the reaction vessel during CVD, thus simplifying the process and reducing production costs.

[0042] In some embodiments, a secondary sintering is performed after deposition. The temperature of the secondary sintering is controlled at 300-500℃ and the time is controlled at 6-24h. After the secondary sintering, a sodium iron sulfate cathode material uniformly coated with conductive carbon is obtained.

[0043] like Figure 2As shown, in this embodiment, sodium sulfate and ferrous sulfate heptahydrate are placed in a vacuum rotary tube furnace for chemical vapor deposition at a specific molar ratio. Argon gas is introduced for protection, and the sintering temperature and time are controlled. After sintering, a carbon source and carrier gas are introduced, and conductive carbon material is deposited through chemical vapor deposition within a specific temperature range while controlling the gas flow rate and deposition time. After deposition, a second sintering is performed to obtain a sodium sulfate-ferrous sulfate composite cathode material with a specific thickness of conductive carbon uniformly coated.

[0044] This embodiment eliminates the need to pre-remove the water of crystallization from ferrous sulfate heptahydrate. Instead, it increases the inert gas flow rate during the vacuum rotary kiln sintering process and blows out water vapor as the furnace gradually heats up. This method simplifies the commercial synthesis process and facilitates mass production. Furthermore, this embodiment achieves a one-step coating of conductive carbon material onto the sintered sodium ferric sulfate composite material via chemical vapor deposition. Compared to ball milling the conductive carbon material and the sodium ferric sulfate composite material, this process solves the uniformity problem of the conductive carbon material when coating the sodium ferric sulfate composite material, thus improving the electrochemical performance of the composite material. Simultaneously, combining the sintering and deposition processes simplifies the synthesis of this cathode material, reduces time consumption, optimizes the synthesis process, and decreases industrial production costs.

[0045] This invention also provides a composite cathode material, prepared using the aforementioned method. The prepared composite cathode material, through chemical vapor deposition, achieves a one-step coating of conductive carbon material onto the sintered sodium ferric sulfate composite material. This solves the uniformity problem of the conductive carbon material during the coating of the sodium ferric sulfate composite material, improves the electrochemical performance of the composite material, addresses the issues of poor conductivity and water absorption in cathode materials, enhances the specific capacity of the cathode material, and improves issues such as poor cycle life and rate performance.

[0046] This invention also provides an application of composite cathode material as cathode material in sodium-ion batteries.

[0047] The present invention will be further illustrated below through specific embodiments.

[0048] Example 1

[0049] This embodiment prepares a sodium ferric sulfate composite cathode material uniformly coated with conductive carbon material. The specific steps include:

[0050] Sodium sulfate and ferrous sulfate heptahydrate were placed in a 1:2 molar ratio in a 5L rotary tube furnace. The sintering temperature was controlled at 350℃ for 12 hours, and the flow rate of the protective argon gas was 3L / min. After sintering, a conductive carbon material deposition process was performed. During this process, a mixed gas consisting of acetylene (carbon source) and argon (carrier gas) was introduced at a flow rate of 0.1L / min. The carbon source content was 5%. The deposition temperature was 350℃, and the deposition time was 1 hour. After deposition, a sodium ferric sulfate composite material with a carbon-coated layer thickness of 20nm was obtained. A second sintering process was then performed at 350℃ for 12 hours to finally obtain the composite cathode material, denoted as Na2Fe2(SO4)3·C. 20 .

[0051] Example 2

[0052] The difference between this embodiment and Embodiment 1 is that the flow rates of the carbon source and carrier gas during the chemical vapor deposition process are adjusted to 0.2 L / min. After the second sintering is completed, the resulting sodium iron sulfate composite cathode material with a carbon coating thickness of 40 nm is denoted as Na2Fe2(SO4)3·C 40 .

[0053] Example 3

[0054] The difference between this embodiment and Embodiment 1 is that the flow rates of the carbon source and carrier gas during the chemical vapor deposition process are adjusted to 0.5 L / min. After the second sintering is completed, the resulting sodium iron sulfate composite cathode material with a carbon coating thickness of 100 nm is denoted as Na2Fe2(SO4)3·C 100 .

[0055] Example 4

[0056] The difference between this embodiment and Embodiment 1 is that the carbon source in the chemical vapor deposition process is adjusted to methane to prepare a sodium iron sulfate composite cathode material. The thickness of the carbon coating layer of this composite material is 10 nm, denoted as Na2Fe2(SO4)3·C 010 .

[0057] Example 5

[0058] The difference between this embodiment and Embodiment 4 is that the flow rates of the carbon source and carrier gas during the chemical vapor deposition process are adjusted to 0.2 L / min. After the second sintering is completed, the resulting sodium iron sulfate cathode composite material with a carbon coating thickness of 20 nm is denoted as Na2Fe2(SO4)3·C 020 .

[0059] Example 6

[0060] The difference between this embodiment and Embodiment 5 is that the flow rates of the carbon source and carrier gas during the chemical vapor deposition process are adjusted to 0.5 L / min. After the second sintering is completed, the resulting sodium iron sulfate cathode composite material with a carbon coating thickness of 50 nm is denoted as Na2Fe2(SO4)3·C 050 .

[0061] Example 7

[0062] The difference between this embodiment and Example 1 is that the carbon source is changed to acetone to prepare a sodium iron sulfate composite cathode material. The thickness of the carbon coating layer of this composite material is 30 nm, denoted as Na2Fe2(SO4)3·C 0030 .

[0063] Example 8

[0064] The difference between this embodiment and Embodiment 6 is that the flow rates of the carbon source and carrier gas during the chemical vapor deposition process are adjusted to 0.2 L / min. After the second sintering is completed, the resulting sodium iron sulfate cathode composite material with a carbon coating thickness of 60 nm is denoted as Na2Fe2(SO4)3·C 0060 .

[0065] Example 9

[0066] The difference between this embodiment and Embodiment 6 is that the flow rates of the carbon source and carrier gas during the chemical vapor deposition process are adjusted to 0.5 L / min. After the second sintering is completed, the resulting sodium iron sulfate cathode composite material with a carbon coating thickness of 150 nm is denoted as Na2Fe2(SO4)3·C 00150 .

[0067] Application Examples:

[0068] The carbon-coated sodium iron sulfate composite cathode materials obtained in each embodiment were mixed with a conductive agent (acetylene black) and a binder (PVDF) in a mass ratio of 8:1:1, and a certain amount of NMP was added to prepare cathode slurries. These slurries were then uniformly coated onto aluminum foil and dried before being cut into 12mm diameter circular cathode sheets. A 14mm diameter, 0.5mm thick sodium metal sheet was used as the negative electrode, and a 16mm diameter GF / D glass fiber sheet was used as the separator. A 1mol / L NaClO4 solution in PC was used as the electrolyte. Button-type sodium-ion batteries were assembled in a glove box with a water and oxygen content of less than 0.01ppm. The electrochemical performance of the synthesized modified materials was tested within a voltage range of 2.0V-4.5V.

[0069] Figure 3 The image shows the XRD pattern of the composite cathode material synthesized in Example 1. Based on the XRD diffraction peak shape, it can be demonstrated that the carbon coating did not alter the crystal structure of the sodium ferric sulfate material. Furthermore, the sharp XRD diffraction peaks indicate that the synthesized material has good crystallinity.

[0070] Figure 4 The diagram shows the charge-discharge curves of Example 1 at a voltage range of 2.0V-4.5V and a current density of 0.1C (12mA / g). Figure 4 As can be seen from the example, the specific capacity in Example 1 is well performed, proving that carbon can be coated on the surface of sodium ferric sulfate material by chemical vapor deposition to improve its electrochemical performance.

[0071] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for preparing a composite cathode material, characterized by, The application relates to a preparation method of a composite positive electrode material. Sodium sulfate and ferrous sulfate heptahydrate are put into a reaction container, and primary sintering is carried out under a protective atmosphere to obtain sodium iron sulfate intrinsic material; A mixed gas of a carbon source and a carrier gas is introduced into the reaction container, a conductive carbon material is coated on the sodium iron sulfate intrinsic material by using a chemical vapor deposition method, and secondary sintering is carried out to obtain the composite positive electrode material.

2. The method of claim 1, wherein the composite cathode material is prepared by the steps of: mixing a lithium transition metal oxide, a lithium source, and a lithium ion source; and sintering the mixture. The flow rate of the mixed gas is controlled to be 0.1-0.5 L / min, the deposition temperature of the chemical vapor deposition is controlled to be 300-500 DEG C, and the deposition time is controlled to be 0.1-10 h.

3. The method of claim 2, wherein the lithium transition metal composite cathode material is prepared by the following steps: The volume fraction of the carbon source in the mixed gas is controlled to be 5-8%. ​ 4. The method of claim 3, wherein the lithium transition metal composite cathode material is prepared by the following steps of: The carbon source comprises one of acetylene, methane and acetone. ​ 5. The method of claim 1, wherein the composite cathode material is prepared by the steps of: mixing a lithium transition metal oxide, a lithium source, and a lithium ion source; and sintering the mixture. The flow rate of the protective atmosphere is controlled to be 1-10 L / min.

6. The method of claim 1, wherein the composite cathode material is prepared by the steps of: mixing a lithium metal oxide, a carbon material, and a binder to form a mixture; and coating the mixture on a current collector to form a cathode. The temperature of the primary sintering is controlled to be 300-500 DEG C, and the time is controlled to be 6-24 h.

7. The method of claim 1, wherein the composite cathode material is prepared by the steps of: mixing a lithium metal oxide, a carbon material, and a binder to form a mixture; and coating the mixture on a current collector to form a cathode. The amount of substance of the sodium sulfate is x, the amount of substance of the ferrous sulfate heptahydrate is y, and the ratio of x to y satisfies the following relation: 0.1<=x / y<=4, 2<=x+2y<=100.

8. The method of claim 1, wherein the composite cathode material is prepared by a process comprising: mixing a lithium metal oxide, a conductive material, and a binder to form a mixture; and coating the mixture on a current collector to form the composite cathode material. The temperature of the secondary sintering is controlled to be 300-500 DEG C, and the time is controlled to be 6-24 h.

9. A composite cathode material, characterized in that, The composite positive electrode material is prepared by using the preparation method of any one of claims 1-8.

10. Use of a composite cathode material, characterized in that The composite positive electrode material of claim 9 is used as a positive electrode material of a sodium ion battery.

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