A porous hollow carbon sphere / sodium ferrite sulfate composite material and preparation and application in sodium ion battery

Abstract

The application discloses a kind of porous hollow carbon sphere / sodium sulfate ferrous sulfate composite material and preparation and application of sodium ion battery, it is related to electrode material technical field.The method includes that sodium sulfate, ferrous sulfate, reducing agent mixed solution is prepared according to certain proportion, it is mixed with porous hollow carbon sphere, precursor is obtained by drying;In inert atmosphere, precursor powder is heated to predetermined sintering temperature and keeps warm for a period of time, and porous hollow carbon sphere / sodium sulfate ferrous sulfate composite material is obtained.The sodium sulfate ferrous sulfate composite material that is formed body contact with the conductive carbon framework is prepared by the capillary adsorption of porous hollow carbon sphere in the application, can effectively realize the limited anchoring of nanoscale sodium sulfate ferrous sulfate particles in porous hollow carbon sphere, promote the rapid transmission of sodium ion and electron, significantly improve its reversible sodium storage capacity, rate performance and cycle life.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology, specifically to a porous hollow carbon sphere / sodium iron sulfate composite material, its preparation, and its application in sodium-ion batteries. Background Technology

[0002] In recent years, with the rising demand for large-scale energy storage equipment, the rapid depletion of fossil fuels, and the soaring price of lithium metal, sodium-ion batteries, developed concurrently with lithium-ion batteries, have once again become a research hotspot. Compared to lithium-ion batteries, sodium-ion batteries offer numerous advantages, including abundant raw materials, low cost, high safety, long lifespan, and good stability. Especially in the field of large-scale grid energy storage, where energy density is no longer the primary consideration for battery performance, the research and application of sodium-ion batteries can significantly alleviate the equipment shortage in energy storage and drive continuous innovation and resource optimization in the battery technology industry. Meanwhile, sodium-ion batteries have already demonstrated superior performance in various industries, including new energy vehicles and power tool applications. However, the development of high-performance cathode materials remains a major obstacle to the further commercialization of sodium-ion batteries.

[0003] Polyanionic cathode materials are diverse, low-cost, and possess tunable structures, stable frameworks, and three-dimensional sodium-ion diffusion channels. Furthermore, the inductive effect generated by the anionic groups gives them a series of advantages compared to transition metal oxides and Prussian blue analogs, including superior stability, high redox potential, and minimal volume change during charge and discharge. Compared to other polyanionic materials, sulfate anionic groups have stronger electronegativity, resulting in a stronger inductive effect; sodium ferric sulfate is a representative material with a high voltage plateau. Sodium ferric sulfate is inexpensive to prepare and can be prepared using various methods. Its three-dimensional structure provides a stable and rapid transport channel for sodium ions and electrons, effectively reducing volume change during charge and discharge. Simultaneously, sodium ferric sulfate has a high theoretical specific capacity, implying excellent energy density (exceeding 350 Wh / kg). The advantages of a high voltage plateau, large theoretical capacity, and low raw material cost demonstrate that sodium ferric sulfate has sufficient potential to become a low-cost, high-performance cathode material for sodium-ion batteries.

[0004] However, sulfate materials are highly sensitive to environmental conditions during synthesis and storage. Direct contact with air, high humidity, and temperatures above 450°C can all cause the ferrous iron in sodium ferric sulfate to oxidize or undergo phase transition decomposition. Therefore, strict environmental control and the addition of reducing agents are necessary during synthesis and storage. Secondly, sodium ferric sulfate itself has poor conductivity and a low synthesis temperature, requiring composite formation with various conductive carbons to ensure excellent electronic and ionic conductivity. While those skilled in the art have prepared sodium ferric sulfate composites using methods such as ball milling or spray drying, they have failed to adequately control the composite state of conductive carbon and sodium ferric sulfate. The two often form point-to-surface contact rather than volumetric contact, and the resulting sodium ferric sulfate particles are relatively large, leading to poor composite effects with conductive carbon. In summary, large-particle sodium ferric sulfate and its uneven contact with conductive carbon are detrimental to the electrochemical utilization rate at the subsequent battery level.

[0005] Therefore, based on the above problems, there is an urgent need to invent a method that is simple in process, safe, and can enable sodium ferric sulfate to contact conductive carbon formations and control their particle size in order to prepare sodium ferric sulfate materials with excellent electrochemical performance. Summary of the Invention

[0006] To address the shortcomings of the aforementioned background technology, this invention provides a porous hollow carbon sphere / sodium iron sulfate composite material, its preparation, and its application in sodium-ion batteries. This method utilizes the capillary adsorption of porous hollow carbon spheres to adsorb and fill the numerous pores inside and on the surface of the spheres with an aqueous precursor. After drying, the nanoscale intermediate particles are tightly anchored inside and on the surface of the porous hollow carbon spheres. After sintering, the intermediate phase transforms into the active material, sodium iron sulfate. The three-dimensional conductive framework of the porous hollow carbon spheres and the sodium iron sulfate particles form an active network integrating electron and ion transport.

[0007] The first objective of this invention is to provide a porous hollow carbon sphere / sodium ferric sulfate composite material, the composite material comprising porous hollow carbon spheres and sodium ferric sulfate loaded on the porous hollow carbon spheres;

[0008] The sodium ferric sulfate loading is 5 to 20 times the mass of the porous carbon spheres.

[0009] Preferably, the porous hollow carbon spheres have a diameter of 150-250 nm and a specific surface area of ​​800-1000 m². 2 g -1 .

[0010] Preferably, the sodium ferric sulfate has a particle size of 10~50 nm.

[0011] The second objective of this invention is to provide a method for preparing a porous hollow carbon sphere / sodium ferric sulfate composite material, comprising the following steps:

[0012] Sodium sulfate, ferrous sulfate and a reducing agent are uniformly dispersed in an aqueous solvent in a certain proportion to obtain a precursor solution;

[0013] The precursor solution was mixed with porous hollow carbon spheres and dried to obtain the intermediate.

[0014] In an inert atmosphere, the intermediate is heated to a predetermined temperature for sintering and held at that temperature for a period of time to obtain a porous hollow carbon sphere / sodium iron sulfate composite material.

[0015] Preferably, the molar ratio of sodium sulfate to ferrous sulfate is 1:1.0~1.4; the molar ratio of ferrous sulfate to reducing agent is 1:0.1~0.5; and the mass fraction of the porous hollow carbon spheres is 1%~15%.

[0016] Preferably, the reducing agent is one or more selected from ascorbic acid, oxalic acid, glucose, citric acid, sodium oxalate, and sodium citrate.

[0017] Preferably, when the intermediate is heated to a predetermined temperature, the heating rate is 0.5~10℃ / min; the predetermined temperature is 300~450℃, and the holding time is 8~48 h.

[0018] Preferably, the drying method is evaporative drying, spray drying, or freeze drying; the drying temperature is 60~180℃, and the drying time is 12~24h.

[0019] Preferably, the inert atmosphere is argon and / or nitrogen.

[0020] The third objective of this invention is to provide an application of a porous hollow carbon sphere / sodium iron sulfate composite material in sodium-ion batteries.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention provides a porous hollow carbon sphere / sodium ferric sulfate composite material, its preparation, and its application in sodium-ion batteries. The raw materials used in this invention are porous hollow carbon spheres, sodium sulfate, ferrous sulfate, and a reducing agent, all of which are widely available. The preparation method of this invention does not require dehydration treatment of hydrated ferrous sulfate or the use of various costly equipment or chemicals. It is simple and safe to operate, fully maintaining the advantages of low cost and high safety of polyanionic sulfate materials, and conforming to the green ecological concept of sustainable development. Compared with other carbon composite methods, the method provided by this invention, after thoroughly mixing the porous hollow carbon spheres with the precursor solution before drying, stably confines the intermediate substance within the pores of the porous hollow carbon spheres through capillary adsorption. This minimizes the particle size and agglomeration of active particles, greatly enhancing the ion and electron transport capabilities between sodium ferric sulfate particles and between sodium ferric sulfate and the carbon matrix, thus maximizing its electrochemical performance. This invention proposes a method for preparing a composite material with porous hollow carbon spheres. This method requires no additional hazardous chemicals, is safe and environmentally friendly, uses widely available raw materials, and has a simple preparation process. The resulting porous hollow carbon sphere / sodium ferric sulfate composite material exhibits excellent performance and is suitable for large-scale commercial production. Attached Figure Description

[0023] Figure 1 This is a scanning electron microscope (SEM) image of the porous hollow carbon sphere / sodium iron sulfate composite material prepared in Example 1.

[0024] Figure 2 The image shows the XRD pattern of the porous hollow carbon sphere / sodium iron sulfate composite material prepared in Example 1.

[0025] Figure 3 The charge-discharge curves of the porous hollow carbon sphere / sodium iron sulfate composite material prepared in Example 1 at a current density of 0.1C are shown.

[0026] Figure 4 The graph shows the cycling performance of the porous hollow carbon sphere / sodium iron sulfate composite material prepared in Example 1 at a current density of 0.5C.

[0027] Figure 5 The graph shows the rate performance of the porous hollow carbon sphere / sodium iron sulfate composite material prepared in Example 1 at different current densities from 0.1C to 20C.

[0028] Figure 6 The graph shows the rate performance of the sodium ferric sulfate material prepared in Comparative Example 1 at different current densities from 0.1C to 20C.

[0029] Figure 7 This is a schematic diagram of the structure of the composite material provided by the present invention. Detailed Implementation

[0030] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0031] This invention addresses the problems of low capacity, poor composite effect with conductive carbon, large particle size, and numerous steps in the preparation of sodium ferric sulfate cathode materials currently available. The proposed method involves: adsorption: mixing the precursor in an aqueous solution with porous hollow carbon spheres, performing capillary adsorption, and then drying; sintering: heating the dried powder to a predetermined temperature under an inert atmosphere for sintering, thus obtaining the porous hollow carbon sphere / sodium ferric sulfate composite material. This method is simple, safe to operate, and produces materials with excellent electrochemical performance, making it suitable for large-scale commercial applications.

[0032] To achieve the above objectives, the first aspect of the present invention provides a porous hollow carbon sphere / sodium ferric sulfate composite material, see [link to previous document]. Figure 7 As shown, the composite material includes porous hollow carbon spheres and sodium ferric sulfate loaded on the porous hollow carbon spheres;

[0033] The sodium ferric sulfate loading is 5 to 20 times the mass of the porous carbon spheres.

[0034] The porous hollow carbon spheres have a diameter of 150~250 nm and a specific surface area of ​​800~1000 m². 2 g -1 .

[0035] The diameter of the sodium ferric sulfate is 10~50 nm.

[0036] The composite material provided by this invention is based on the capillary adsorption of nano-sized sodium ferric sulfate material inside and on the surface of porous hollow carbon spheres, effectively controlling its particle size. The porous hollow carbon spheres provide a stable structural framework, conductive framework, and ion channels for sodium ferric sulfate, greatly promoting the transport of sodium ions and electrons, thereby significantly improving its reversible specific capacity, rate performance, and cycle life.

[0037] A second aspect of this invention provides a method for preparing a porous hollow carbon sphere / sodium ferric sulfate composite material, comprising the following steps:

[0038] Sodium sulfate, ferrous sulfate and reducing agent are uniformly dispersed in an aqueous solvent in a certain proportion to obtain a precursor solution;

[0039] The precursor solution was mixed with porous hollow carbon spheres and dried to obtain the intermediate.

[0040] In an inert atmosphere, the intermediate is heated to a predetermined temperature for sintering and held at that temperature for a period of time to obtain a porous hollow carbon sphere / sodium iron sulfate composite material.

[0041] This invention utilizes the capillary adsorption of porous hollow carbon spheres to adsorb and fill the numerous pores inside and on the surface of the spheres with an aqueous precursor solution. After drying, the nanoscale intermediate particles are tightly anchored inside and on the surface of the porous hollow carbon spheres. After sintering, the intermediate transforms into the active material sodium ferric sulfate. The three-dimensional conductive framework of the porous hollow carbon spheres and the sodium ferric sulfate particles form an active network integrating electron and ion transport.

[0042] This invention prepares a sodium ferric sulfate composite material in contact with a conductive carbon framework through capillary adsorption of porous hollow carbon spheres. This effectively achieves confined anchoring of nano-sized sodium ferric sulfate particles in porous hollow carbon spheres, promotes rapid transport of sodium ions and electrons, and significantly improves its reversible sodium storage capacity, rate performance, and cycle life.

[0043] The molar ratio of sodium sulfate to ferrous sulfate is 1:1.0~1.4; the molar ratio of ferrous sulfate to reducing agent is 1:0.1~0.5; and the mass fraction of the porous hollow carbon spheres is 1%~15%.

[0044] The reducing agent is one or more of ascorbic acid, oxalic acid, glucose, citric acid, sodium oxalate, and sodium citrate.

[0045] When the intermediate is heated to a predetermined temperature, the heating rate is 0.5~10℃ / min; the predetermined temperature is 300~450℃, and the holding time is 8~48 h.

[0046] The drying method is evaporation drying, spray drying or freeze drying; the drying temperature is 60~180℃ and the drying time is 12~24h.

[0047] The inert atmosphere is argon and / or nitrogen.

[0048] A third aspect of this invention provides the application of a porous hollow carbon sphere / sodium iron sulfate composite material in sodium-ion batteries. Specifically, the porous hollow carbon sphere / sodium iron sulfate composite material provided by this invention is mainly used as a cathode material in sodium-ion batteries.

[0049] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0050] Porous hollow carbon spheres were prepared using a common silica hard template method: 24 mmol of tetrapropyl orthosilicate was added to a mixture containing 140 ml of ethanol, 20 ml of deionized water, and 6 ml of ammonia (25 wt%). 1.6 g of resorcinol, 2.24 ml of formaldehyde (37 wt%), and 2.0 g of thiourea were dissolved in the above solution. The mixture was stirred for 24 hours, washed with water and ethanol, and dried at 80 °C. The resulting product was carbonized at 900 °C for 4 hours under a protective atmosphere. Finally, it was immersed in hydrofluoric acid (25 wt%) for 24 hours, then filtered with water. Porous hollow carbon spheres were obtained by drying at 80 °C.

[0051] Example 1

[0052] A method for preparing a porous hollow carbon sphere / sodium ferric sulfate composite material includes the following steps:

[0053] (1) Anhydrous sodium sulfate, ferrous sulfate heptahydrate, and ascorbic acid in a molar ratio of 1.25:1.4:0.5 were dissolved in a small amount of deionized water. 10% (w / w) of porous hollow carbon spheres were added for adsorption. After thorough adsorption and mixing, the mixture was dried in a 60℃ oven for 12 hours. The porous hollow carbon spheres had a diameter of approximately 200 nm and a specific surface area of ​​800 m². 2 g -1 .

[0054] (2) The dried intermediate powder was placed in an atmosphere furnace and heated to 350°C at a rate of 5°C / min under an argon atmosphere. The temperature was maintained for 12 hours and then naturally cooled to room temperature to obtain a porous hollow carbon sphere / sodium iron sulfate composite material. The loading of sodium iron sulfate in the final prepared electrode was 10 times the mass of the porous carbon spheres.

[0055] Example 2

[0056] A method for preparing a porous hollow carbon sphere / sodium ferric sulfate composite material includes the following steps:

[0057] (1) Anhydrous sodium sulfate, ferrous sulfate heptahydrate, and glucose in a molar ratio of 1.1:1.4:0.4 were dissolved in a small amount of deionized water. 5% by mass of porous hollow carbon spheres were added for adsorption. After thorough adsorption and mixing, the mixture was dried at 150°C using a spray drying method. The porous hollow carbon spheres had a diameter of approximately 250 nm and a specific surface area of ​​1000 m². 2 g -1 .

[0058] (2) The dried intermediate powder was placed in an atmosphere furnace and heated to 380°C at a rate of 10°C / min under an argon atmosphere. The temperature was maintained for 10 hours and then naturally cooled to room temperature to obtain a porous hollow carbon sphere / sodium iron sulfate composite material. The loading of sodium iron sulfate in the final prepared electrode was 20 times the mass of the porous carbon spheres.

[0059] Example 3

[0060] A method for preparing a porous hollow carbon sphere / sodium ferric sulfate composite material includes the following steps:

[0061] (1) Anhydrous sodium sulfate, ferrous sulfate pentahydrate, and citric acid in a molar ratio of 1:1.2:0.3 were dissolved in a small amount of deionized water. Porous hollow carbon spheres (15% by mass) were added for adsorption. After thorough adsorption and mixing, the mixture was dried using a freeze-drying apparatus. The porous hollow carbon spheres had a diameter of approximately 50 nm and a specific surface area of ​​950 m². 2 g -1 .

[0062] (2) The dried intermediate powder was placed in an atmosphere furnace and heated to 400°C at a rate of 3°C / min under a nitrogen atmosphere. The temperature was maintained for 18 hours and then naturally cooled to room temperature to obtain a porous hollow carbon sphere / sodium iron sulfate composite material. The loading of sodium iron sulfate in the final prepared electrode was 6 times the mass of the porous carbon spheres.

[0063] Compare with Example 1

[0064] A method for preparing a sodium ferric sulfate material without porous hollow carbon spheres includes the following steps:

[0065] (1) Dissolve anhydrous sodium sulfate, ferrous sulfate monohydrate and oxalic acid in a molar ratio of 1.3:1.4:0.2 in a small amount of deionized water. Dry in an oven at 80℃ for 24 hours.

[0066] (2) The dried intermediate powder was placed in an atmosphere furnace and heated to 400°C at a rate of 3°C / min under an argon atmosphere. The temperature was held for 14 hours and then naturally cooled to room temperature to obtain sodium iron sulfate material without porous hollow carbon spheres.

[0067] To illustrate the relevant properties of the porous hollow carbon sphere / sodium ferric sulfate composite material provided by the present invention, the accompanying drawings are provided.

[0068] Figure 1This is a scanning electron microscope (SEM) image of the porous hollow carbon sphere / sodium ferric sulfate composite material prepared in Example 1. A small portion of the prepared sodium ferric sulfate material is adsorbed on the surface of the porous hollow carbon spheres, while the majority exists within the internal pores of the spheres. This bulk contact structure provides a rapid channel for the transport of electrons and sodium ions, and combined with the conductive framework of the porous hollow carbon spheres themselves, it effectively enhances their various electrochemical properties.

[0069] Figure 2 The image shows the XRD pattern of the porous hollow carbon sphere / sodium ferric sulfate composite material prepared in Example 1. All characteristic peaks match well with the sodium ferric sulfate material, and no obvious impurity phases are present, indicating that the preparation method of this invention does not damage the crystal structure of sodium ferric sulfate.

[0070] Combination Figure 1 and Figure 2 Analysis shows that the preparation method of this invention can effectively prevent the oxidation of ferrous iron in sodium ferric sulfate because the porous hollow carbon spheres provide a robust conductive framework and a reducing environment, resulting in high-purity sodium ferric sulfate material. Most of the sodium ferric sulfate material occupies a large number of pores in the porous hollow carbon spheres, forming a three-dimensional framework with considerable volumetric contact.

[0071] To illustrate the application of the porous hollow carbon sphere / sodium iron sulfate composite material prepared in this invention in sodium-ion batteries, the composite material provided in Example 1 was used as the positive electrode material in a sodium-ion battery for sodium-ion battery assembly and electrochemical performance testing:

[0072] The battery electrode was prepared by uniformly grinding the porous hollow carbon sphere / sodium iron sulfate composite material prepared in Example 1 with Ketjen black and polyvinylidene fluoride in a mortar with an appropriate amount of N-methylpyrrolidone in a mass ratio of 8:1:1, and then coating it onto aluminum foil. The resulting material was then dried in a vacuum drying oven at 120°C for 12 hours and cut into 12mm diameter electrode sheets. The separator used for battery assembly was a glass fiber separator, the electrolyte was 1M NaClO4 ester-based electrolyte + 5% FEC, and the counter electrode was a sodium sheet. After standing for 12 hours, constant current charge-discharge tests were performed at different current densities.

[0073] Figure 3The first charge-discharge curve of the porous hollow carbon sphere / sodium ferric sulfate composite material prepared in Example 1 is shown at a current density of 0.1C. This porous hollow carbon sphere / sodium ferric sulfate composite material exhibits a reversible specific capacity of 122.4 mAh / g and an energy density exceeding 400 Wh / kg, significantly higher than similar products. The porous hollow carbon spheres and the sodium ferric sulfate adsorbed within and on their surface form excellent bulk contact, and the combined framework provides a rapid transfer channel for electrons and ions, greatly releasing the electrochemical potential of sodium ferric sulfate. This demonstrates the feasibility and effectiveness of constructing a porous hollow carbon sphere / sodium ferric sulfate composite material to improve its electrochemical performance.

[0074] Figure 4 The graph shows the cycling performance of the porous hollow carbon sphere / sodium ferric sulfate composite material prepared in Example 1 at a current density of 0.5C. After 100 cycles at 0.5C, the porous hollow carbon sphere / sodium ferric sulfate composite material of Example 1 retained 84.6% of its capacity, exhibiting excellent cycling stability. This is because the porous hollow carbon spheres provide an additional carbon framework to promote particle transport and provide better support, effectively buffering volume changes during continuous charge and discharge.

[0075] Figure 5 The graph shows the rate performance of the porous hollow carbon sphere / sodium ferric sulfate composite material prepared in Example 1 at different current densities from 0.1C to 20C. The porous hollow carbon sphere / sodium ferric sulfate composite material prepared in Example 1 also exhibits excellent rate performance, maintaining a reversible capacity of 65 mAh / g at 20C. When the current density recovers to 0.1C, the reversible capacity is 110.4 mAh / g, reaching 93.2% of the initial capacity. This demonstrates the superiority of the carbon framework and sodium ferric sulfate composite material formed by the present invention in forming a close-packed contact, greatly improving its electrochemical reaction kinetics.

[0076] Figure 6 This is a rate performance graph of the sodium ferric sulfate material prepared in Comparative Example 1 at different current densities from 0.1C to 20C. (Compared to...) Figure 5 The porous hollow carbon sphere / sodium ferric sulfate composite material of Example 1 serves as a comparison. The control sample had a reversible capacity of 92 mAh / g at 0.1C, but its capacity decayed rapidly with increasing current density, and it had almost no discharge capacity at 20C. The comparative results show that the sodium storage performance of the porous hollow carbon sphere / sodium ferric sulfate composite material of this invention is greatly improved compared to the sodium ferric sulfate material itself.

[0077] This invention describes preferred embodiments and their effects. However, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to include both the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0078] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A porous hollow carbon sphere / sodium ferric sulfate composite material, characterized in that, The composite material includes porous hollow carbon spheres and sodium ferric sulfate loaded on the porous hollow carbon spheres; wherein, sodium ferric sulfate is adsorbed inside and on the surface of the porous hollow carbon spheres; The sodium ferric sulfate loading is 5 to 20 times the mass of the porous carbon spheres; The porous hollow carbon spheres have a diameter of 150~250 nm and a specific surface area of ​​800~1000 m². 2 g -1 ; The particle size of the sodium ferric sulfate is 10~50 nm; The porous hollow carbon sphere / sodium ferric sulfate composite material is prepared according to the following steps: Sodium sulfate, ferrous sulfate and a reducing agent are uniformly dispersed in an aqueous solvent in a certain proportion to obtain a precursor solution; The precursor solution was mixed with porous hollow carbon spheres and dried to obtain the intermediate. In an inert atmosphere, the intermediate is heated to a predetermined temperature for sintering and held at that temperature for a period of time to obtain a porous hollow carbon sphere / sodium iron sulfate composite material. When the intermediate is heated to a predetermined temperature, the heating rate is 0.5~10℃ / min; the predetermined temperature is 300~450℃, and the holding time is 8~48 h.

2. A method for preparing the porous hollow carbon sphere / sodium ferric sulfate composite material according to claim 1, characterized in that, Includes the following steps: Sodium sulfate, ferrous sulfate and a reducing agent are uniformly dispersed in an aqueous solvent in a certain proportion to obtain a precursor solution; The precursor solution was mixed with porous hollow carbon spheres and dried to obtain the intermediate. In an inert atmosphere, the intermediate is heated to a predetermined temperature for sintering and held at that temperature for a period of time to obtain a porous hollow carbon sphere / sodium iron sulfate composite material. When the intermediate is heated to a predetermined temperature, the heating rate is 0.5~10℃ / min; the predetermined temperature is 300~450℃, and the holding time is 8~48 h.

3. The method for preparing the porous hollow carbon sphere / sodium ferric sulfate composite material according to claim 2, characterized in that, The molar ratio of sodium sulfate to ferrous sulfate is 1:1.0~1.4; the molar ratio of ferrous sulfate to reducing agent is 1:0.1~0.5; and the mass fraction of the porous hollow carbon spheres is 1%~15%.

4. The method for preparing the porous hollow carbon sphere / sodium ferric sulfate composite material according to claim 2, characterized in that, The reducing agent is one or more of ascorbic acid, oxalic acid, glucose, citric acid, sodium oxalate, and sodium citrate.

5. The method for preparing the porous hollow carbon sphere / sodium ferric sulfate composite material according to claim 2, characterized in that, The drying method is evaporation drying, spray drying or freeze drying; the drying temperature is 60~180℃ and the drying time is 12~24h.

6. The method for preparing the porous hollow carbon sphere / sodium ferric sulfate composite material according to claim 2, characterized in that, The inert atmosphere is argon and / or nitrogen.

7. The application of the porous hollow carbon sphere / sodium iron sulfate composite material as described in claim 1 in a sodium-ion battery.

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