Sulfur-doped starch-based porous hard carbon material as well as preparation method and application thereof

Abstract

The invention discloses a sulfur-doped starch-based porous hard carbon material, a preparation method thereof and application of the sulfur-doped starch-based porous hard carbon material in a sodium-ion battery. The particle size D50 of the material is 2-15 [mu] m, the mesoporous volume is 0.10-0.40 cm < 3 > / g, the average pore size is 5-35 nm, the pore size range is 0.5-100 nm, and the sulfur element accounts for 0.5-5 wt% of the sulfur-doped hard carbon material. By reasonably controlling the pore size in the precursor, the generation of a macroporous structure which is not beneficial to sodium ion storage in the subsequent carbonization process is avoided, so that the optimization of the contrast surface area, the defect site and the closed pore structure is realized, and the sulfur-doped porous hard carbon material with good electrochemical performance is designed. The hard carbon material used as the negative electrode material of the sodium ion battery has the advantages of high reversible specific capacity and high first coulombic efficiency, keeps relatively high rate capability of a porous structure, and has a good application prospect in the application of the sodium ion battery.

Description

Technical Field

[0001] The invention belongs to the field of battery materials, and particularly relates to a sulfur-doped starch-based porous hard carbon material, a preparation method thereof, and an application thereof in a sodium ion battery. Background Art

[0002] For a long time, fossil energy has been the main energy source in the field of energy utilization, and the environmental problems it brings have hindered the development of human society. The emergence of renewable clean energy such as solar energy, wind energy, and tidal energy has alleviated the energy problem to a certain extent. In order to integrate these renewable clean energy sources into the power grid, large-scale energy storage systems are a key link. Secondary batteries are a promising large-scale energy storage method with the advantages of flexibility, high energy density and simple maintenance. At present, lithium-ion batteries are a common energy storage power source. As commercial batteries for electric vehicles, they can reduce dependence on fossil energy. Lithium is an important component of lithium-ion batteries. However, lithium is unevenly dispersed in the earth's crust. Due to its limited reserves, the price of lithium has been rising. In comparison, sodium-ion batteries have the advantages of abundant raw material resources, low cost, safety and good low-temperature performance. They have broad application prospects in electric two-wheeled vehicles, low-speed electric vehicles and large-scale energy storage.

[0003] Sodium-ion batteries are mainly composed of positive electrodes, negative electrodes, electrolytes and separators. Their working principle is the embedding and de-embedding of sodium ions in positive and negative electrode materials to achieve energy charging and release. The positive and negative electrode materials determine the battery's operating voltage, energy density, cycle stability and rate performance. Compared with positive electrode materials, the development of negative electrode materials for sodium-ion batteries is relatively slow. Graphite negative electrode materials suitable for lithium-ion batteries are not suitable for sodium-ion batteries.

[0004] Heteroatom-doped porous carbon has many advantages as the negative electrode of sodium-ion batteries. First, the well-developed pore structure of porous carbon has abundant internal defect sites, which can provide reaction sites for electrochemical reactions, thereby improving the storage capacity of sodium. It is a feasible method to prepare high-performance porous hard carbon materials using porous precursors. Studies have shown that the high-temperature carbonization stage is accompanied by the development of graphite domains, which will shrink part of the open-pore structure in the precursor and transform it into a closed-pore structure. The closed-pore structure can increase the low-pressure platform capacity of the hard carbon material, thereby increasing the sodium storage capacity of the sodium-ion battery. Secondly, sulfur atom doping has a positive effect on the improvement of the sodium storage performance of hard carbon materials. Sulfur atoms have a large atomic radius that can effectively expand the interlayer spacing of hard carbon, which is beneficial to the embedding and extraction of sodium ions in hard carbon materials, thereby promoting the improvement of the sodium storage performance of hard carbon materials.

[0005] Although the larger specific surface area of ​​porous carbon can provide more active sites for sodium storage, it will also form more solid electrolyte interface (SEI) films on the electrode surface, resulting in irreversible capacity loss and reduced initial efficiency in the first cycle. Therefore, it is still necessary to develop new negative electrode materials for sodium ion batteries. Summary of the invention

[0006] Based on the above technical background, the present invention reasonably controls the pore size in the precursor, thereby avoiding the formation of a macroporous structure that is not conducive to the storage of sodium ions in the subsequent carbonization process, so as to achieve the optimization of the specific surface area, defect sites and closed-pore structure, and design a sulfur-doped porous hard carbon material with good electrochemical properties. The present invention provides a sulfur-doped starch-based porous hard carbon material and a preparation method thereof. The present invention uses starch as a raw material, and synthesizes sulfur-doped porous starch as a precursor of the hard carbon material by adding a sulfur source in a hydrothermal process. The hydrothermal and solvent exchange processes can fix the natural pores of plant starch to form a mesoporous structure. At the same time, the addition of the sulfur source has a certain regulatory effect on the structure of the pores under high temperature and high pressure. The adjustment of the hydrothermal temperature and time can regulate the pore size of the starch, and the amount of sulfur source added is used to adjust the amount of sulfur doping. Finally, sulfur-doped starch-based hard carbon is obtained by two high-temperature treatments in an inert atmosphere. The first high-temperature treatment is to fix the pore structure of the sulfur-doped porous starch, and the second high-temperature treatment is accompanied by the development of graphite domains, which can shrink part of the open-pore structure in the precursor and convert it into a closed-pore structure. The use of this hard carbon material as the negative electrode material of sodium ion batteries has the advantages of high reversible specific capacity and high first coulombic efficiency, and maintains a high rate performance of the porous structure, and has good application prospects in the application of sodium ion batteries.

[0007] According to the first aspect of the present invention, an object of the present invention is to provide a sulfur-doped porous hard carbon material, wherein the particle size D50 of the material is 2 to 15 μm, and the mesopore volume is 0.10 to 0.40 cm 3 / g, an average pore diameter of 5 to 35 nm, a pore size range of 0.5 to 100 nm, and a proportion of sulfur element in the sulfur-doped hard carbon material of 0.5wt-5wt%.

[0008] Preferably, the mesopore volume of the sulfur-doped porous hard carbon material is 0.13 to 0.35 cm 3 / g, average pore diameter 5 to 30nm, pore size range 1.0 to 50nm.

[0009] Preferably, the mesopore volume of the sulfur-doped porous hard carbon material is 0.17 to 0.26 cm 3 / g, average pore diameter 9.18 to 26.3 nm, pore size range 1.3 to 47.8 nm.

[0010] According to a second aspect of the present invention, an object of the present invention is to provide a method for preparing the sulfur-doped porous hard carbon material, the method comprising:

[0011] 1) Disperse starch in water, add a certain mass of sulfur source and mix, then transfer the mixture to a hydrothermal reactor with a stirring function, first heat it to 70-100°C at 5-10°C / min and keep it warm for 5-20min, control the stirring speed at 500r / min, then heat it to 130-160°C at a heating rate of 5°C / min and keep it warm for 3-6h, and then cool it naturally to room temperature and take it out;

[0012] 2) adding a certain amount of organic solvent to the sulfur-doped porous starch material treated in step 1) to precipitate the sulfur-doped porous starch, filtering and collecting the sulfur-doped porous starch material after sedimentation, and then vacuum drying to obtain the sulfur-doped porous starch material;

[0013] 3) The sulfur-doped porous starch obtained in step 2) is used as a precursor to perform high-temperature carbonization calcination under an inert atmosphere. The calcination process is as follows: first, the temperature is increased from room temperature to 200-500°C at 2-20°C / min, and kept warm for 1-5 hours; then the temperature is increased to 1100-1600°C at 1-10°C / min, and kept warm for 1-5 hours; finally, the temperature is naturally cooled to room temperature to obtain a block hard carbon material.

[0014] Preferably, the starch in step 1) includes, but is not limited to, one or more of corn starch, wheat starch, potato starch, tapioca starch, water chestnut starch, and lotus root starch.

[0015] Preferably, the sulfur source in step 1) includes, but is not limited to, one or more of thiourea, ethanethiol, sulfur powder, and sulfur-containing amino acids, wherein the mass ratio of the sulfur source to starch is 0.1:10 to 5:10.

[0016] Preferably, the organic solvent used in step 2) includes one or more of ethanol, methanol and propanol.

[0017] Preferably, the inert gas used in step 3) is nitrogen, argon or a mixture of the two.

[0018] According to the third aspect of the present invention, an object of the present invention is to provide an application of the sulfur-doped porous hard carbon material as a negative electrode of a sodium ion battery.

[0019] According to a fourth aspect of the present invention, an object of the present invention is to provide a sodium ion battery, wherein the sodium ion battery adopts the sulfur-doped porous hard carbon material as a negative electrode material.

[0020] Beneficial Effects

[0021] The method for preparing sulfur-doped porous hard carbon using starch provided by the present invention has the following advantages:

[0022] 1) Starch is one of the most abundant renewable biomaterials on earth and is widely found in various plants. Compared with other biomass precursors such as cellulose, lignin, and sucrose, starch shows an attractive natural spherical morphology and does not contain ash and salt impurities. It is a competitive candidate in the preparation of carbon materials.

[0023] 2) Without using a template, the natural pores of plant starch are fixed by combining hydrothermal treatment and solvent exchange to form a porous starch precursor with a mesoporous structure. The complex process of removing the template is avoided in the process, and the pore size can be fine-tuned by hydrothermal temperature and time.

[0024] 3) Sulfur-doped hard carbon materials are obtained by introducing sulfur sources into hard carbon precursors for sulfur doping. There is a reversible redox reaction between sodium ions and sulfur atoms. At the same time, sulfur atoms have a large atomic radius, which can effectively expand the interlayer spacing of hard carbon, promote the embedding and de-embedding of sodium ions in hard carbon materials, and improve the reversible specific capacity of sodium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 (a) and (b) are SEM schematic diagrams of hard carbon negative electrode materials synthesized according to the preparation method of Comparative Example 1; Figure 1 (c) and (d) are SEM schematic diagrams of the hard carbon negative electrode material synthesized according to the preparation method of Example 1.

[0027] Figure 2 Schematic diagram of element distribution characterization (EDS) of the hard carbon negative electrode material obtained according to the preparation method of Example 1. DETAILED DESCRIPTION

[0028] Hereinafter, the present invention will be described in detail. Before describing, it should be understood that the terms used in this specification and the appended claims should not be interpreted as being limited to the general meaning and dictionary meaning, but should be interpreted according to the meaning and concept corresponding to the technical aspects of the present invention on the basis of the principle that the inventor is allowed to appropriately define the terms for the best interpretation. Therefore, the descriptions presented here are only preferred examples for illustrative purposes and are not intended to limit the scope of the present invention, so that it should be understood that other equivalents or improvements can be obtained therefrom without departing from the spirit and scope of the present invention.

[0029] In this document, the terms "include", "including", "have", "contain" or any other similar terms are open conjunctions, which are intended to cover non-exclusive inclusions. For example, a composition or product containing multiple elements is not limited to the elements listed herein, but may also include other elements that are not explicitly listed but are generally inherent to the composition or product. In addition, unless otherwise explicitly stated, the term "or" refers to an inclusive "or" rather than an exclusive "or". For example, any of the following situations satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and A and B are both true (or exist). In addition, in this document, the interpretation of the terms "include", "including", "have", and "contain" should be considered to have been specifically disclosed and simultaneously cover closed or semi-closed conjunctions such as "consisting of" and "consisting essentially of".

[0030] In this article, all features or conditions defined in the form of numerical ranges or percentage ranges are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be deemed to have covered and specifically disclosed all possible secondary ranges and individual values ​​within the range, especially integer values. For example, the range description of "1 to 8" should be deemed to have specifically disclosed all secondary ranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, etc., especially secondary ranges defined by all integer values, and should be deemed to have specifically disclosed individual values ​​such as 1, 2, 3, 4, 5, 6, 7, 8, etc. within the range. Unless otherwise specified, the above interpretation method applies to all contents of the entire present invention, regardless of whether the range is broad or not.

[0031] If the quantity or other numerical value or parameter is expressed as a range, a preferred range or a series of upper and lower limits, it should be understood that all ranges consisting of any upper limit or preferred value of the range and the lower limit or preferred value of the range have been specifically disclosed herein, regardless of whether these ranges are disclosed separately. In addition, if a numerical range is mentioned herein, unless otherwise specified, the range should include its endpoints and all integers and fractions within the range.

[0032] In this document, under the premise of achieving the purpose of the invention, numerical values ​​should be understood to have the accuracy of the number of significant digits of the numerical value. For example, the number 40.0 should be understood to cover the range from 39.50 to 40.49.

[0033] In addition, unless otherwise stated, the reagents and solvents disclosed in the article were purchased from Sinopharm Chemical Reagent Co., Ltd. and Duoduo Reagent. The specific surface area analyzer (nitrogen adsorption method) model: ASPA2010 (made in USA) was used to test the pore size distribution range of hard carbon. The blue electric charge and discharge tester model: CT3002A was used to test the charge and discharge specific capacity and first coulomb efficiency of hard carbon materials; the scanning electron microscope model: Czech TESCAN MIRA LMS was used to test the SEM image of hard carbon.

[0034] In step 2) of the preparation method according to the present invention, a certain amount of organic solvent needs to be added to precipitate the sulfur-doped porous starch. This is because polysaccharides are insoluble in alcohol organic solvents and precipitation will occur. After the sulfur-doped porous starch material is precipitated, it is convenient to filter and collect it, and then vacuum dry it to obtain the sulfur-doped porous starch material. The organic solvent can be selected from one or more of ethanol, methanol, and propanol.

[0035] The following examples are only listed as examples of embodiments of the present invention and do not constitute any limitation to the present invention. It can be understood by those skilled in the art that modifications within the scope of the essence and concept of the present invention fall within the scope of protection of the present invention. Unless otherwise specified, the reagents and instruments used in the following examples are all commercially available products.

[0036] Example 1

[0037] 1) Weigh 10 g corn starch and add it to 40 g deionized water and 2 g thiourea. Stir at 500 r / min to evenly disperse the starch in the aqueous solution. Transfer it to a hydrothermal reactor and heat it to 80 °C at 10 °C / min for gelatinization for 10 min. Stir during the process, then heat it to 130 °C at a heating rate of 10 °C / min and keep it for 3 h, and then cool it naturally to room temperature.

[0038] 2) adding 200 g of ethanol to the mixture after the hydrothermal treatment for precipitation, filtering and vacuum drying to obtain sulfur-doped porous starch.

[0039] 3) The sulfur-doped porous starch was transferred to a corundum boat for high-temperature calcination. The calcination process was as follows: first, the temperature was raised to 500°C at 10°C / min and kept at this temperature for 2 hours; then, the temperature was raised to 1300°C at 5°C / min and kept at this temperature for 3 hours; then, the material was naturally cooled to room temperature to obtain a block of hard carbon material. The entire high-temperature carbonization calcination process was carried out in a nitrogen atmosphere with a gas space velocity of 40 mL / min.

[0040] 4) The blocky hard carbon material obtained in step 3) is subjected to oscillation crushing, ball milling and sieving to obtain a hard carbon material product with a particle size of 2 to 15 μm.

[0041] 5) The specific surface area, average pore diameter and micropore size range of the hard carbon material obtained in Example 1 were tested. The detailed results are shown in Table 1.

[0042] pass Figure 1 Figures (c) and (d) show that the hard carbon material obtained in Example 1 has a block-like particle shape with a rough surface and a porous structure. Figure 2 It can be seen from the EDS energy spectrum characterization diagram that the sulfur element is uniformly distributed in the hard carbon material synthesized in Example 1, wherein the weight ratio of the sulfur element to the hard carbon material is approximately 1.64wt%.

[0043] The prepared hard carbon material is used to prepare the negative electrode sheet. The specific conditions for preparing the negative electrode sheet with the hard carbon material are: slurry mass ratio, prepared hard carbon material: carbon black: CMC (carboxymethyl cellulose): SBR (styrene butadiene rubber) = 94:2:2:2, which are mixed to form a slurry, and then coated on copper foil to obtain an electrode sheet with a diameter of 14 mm. Metallic sodium is used as the counter electrode, a glass fiber membrane is used as the diaphragm, and 1M NaPF6 / EC+DEC (volume ratio of 1:1) is used as the electrolyte to assemble a button-type sodium ion battery. The tested voltage range is: 0-2.5V, the test environment temperature is 25°C, and the first charge and discharge test is carried out at 0.1C.

[0044] Example 2

[0045] The process and the remaining steps are the same as those in Example 1, except that 1 g of thiourea is added to the corn starch in this example.

[0046] The hard carbon material prepared in Example 2 was tested according to the same testing method as in Example 1. The testing method, conditions and contents were consistent with those in Example 1.

[0047] Example 3

[0048] The process and the remaining steps are the same as those in Example 1, except that 3 g of thiourea is added to the corn starch in this example.

[0049] The hard carbon material prepared in Example 3 was tested according to the same testing method as in Example 1. The testing method, conditions and contents were consistent with those in Example 1.

[0050] Example 4

[0051] The process and the remaining steps are the same as those in Example 1, except that in this example, after the mixed solution is transferred to the hydrothermal autoclave, it is heated to 70°C at 10°C / min for reaction for 10 min, then heated to 140°C at a heating rate of 10°C / min and kept warm for 3 h, and then naturally cooled to room temperature.

[0052] The hard carbon material prepared in Example 4 was tested according to the same testing method as in Example 1. The testing method, conditions and contents were consistent with those in Example 1.

[0053] Example 5

[0054] The process and the remaining steps are the same as those in Example 1, except that in this example, after the mixed solution is transferred to the hydrothermal autoclave, it is heated to 100°C at 10°C / min for reaction for 10 min, then heated to 150°C at a heating rate of 10°C / min and kept for 3 h, and then naturally cooled to room temperature.

[0055] The hard carbon material prepared in Example 5 was tested according to the same testing method as in Example 1. The testing method, conditions and contents were consistent with those in Example 1.

[0056] Example 6

[0057] The process and the remaining steps are the same as those in Example 1, except that in this example, after the mixed solution is transferred to the hydrothermal autoclave, it is heated to 100°C at 10°C / min for reaction for 10 min, then heated to 160°C at a heating rate of 10°C / min for 3 h, and then naturally cooled to room temperature.

[0058] The hard carbon material prepared in Example 6 was tested according to the same testing method as in Example 1. The testing method, conditions and contents were consistent with those in Example 1.

[0059] Example 7

[0060] The process and the remaining steps are the same as those in Example 1, except that in this example, after the mixed solution is transferred to the hydrothermal autoclave, it is heated to 100°C at 10°C / min for reaction for 10 min, then heated to 150°C at a heating rate of 10°C / min for 8 h, and then naturally cooled to room temperature.

[0061] The hard carbon material prepared in Example 7 was tested according to the same testing method as in Example 1. The testing method, conditions and contents were consistent with those in Example 1.

[0062] Comparative Example 1

[0063] (1) 10g corn starch was transferred into a corundum boat and calcined at high temperature. The calcination process was as follows: first, the temperature was raised to 500°C at 10°C / min and kept at that temperature for 2h; then, the temperature was raised to 1300°C at 5°C / min and kept at that temperature for 3h; then, the temperature was naturally cooled to room temperature to obtain a block of hard carbon material. The entire high-temperature carbonization calcination process was carried out in a nitrogen atmosphere with a gas space velocity of 40mL / min.

[0064] (2) The blocky hard carbon material obtained above is crushed, ball-milled and sieved to obtain a hard carbon material product with a particle size of 2 to 10 μm.

[0065] (3) The hard carbon material prepared in Comparative Example 1 was tested according to the same testing method as in Example 1. The testing method, conditions and contents were consistent with those in Example 1.

[0066] pass Figure 1 It can be seen from the SEM characterization images in (a) and (b) that the hard carbon synthesized in Comparative Example 1 is hard carbon particles with a particle size of 5-20 μm and a smooth surface.

[0067] Comparative Example 2

[0068] The process and the remaining steps are the same as those in Example 1, except that thiourea is not added to the starch solution in this example.

[0069] The hard carbon material prepared in Comparative Example 2 was tested according to the same testing method as in Example 1. The testing method, conditions and contents were consistent with those in Example 1.

[0070] Comparative Example 3

[0071] 10g corn starch and 0.5g thiourea were ground and mixed, then transferred to a corundum boat for high-temperature calcination. The calcination process was as follows: first, the temperature was raised to 500°C at 10°C / min and kept at this temperature for 2h; then the temperature was raised to 1300°C at 5°C / min and kept at this temperature for 3h; then, the temperature was naturally cooled to room temperature to obtain a block of hard carbon material. The entire high-temperature carbonization calcination process was carried out in a nitrogen atmosphere with a gas space velocity of 40mL / min.

[0072] The blocky hard carbon material obtained above is crushed, ball-milled and sieved to obtain a hard carbon material product with a particle size of 2 to 10 μm.

[0073] The hard carbon material prepared in Comparative Example 3 was tested according to the same testing method as in Example 1. The testing method, conditions and contents were consistent with those in Example 1.

[0074] Table 1 Comparison of the performance test results of hard carbon materials obtained in Examples 1 to 7 and Comparative Examples 1 to 3:

[0075]

[0076]

[0077] It can be seen from the implementation data of the above Examples 1 to 7 and the data of Comparative Examples 1 to 3 that the sulfur-doped starch-based porous hard carbon material prepared by the present invention has excellent electrochemical properties and significantly improves the initial charge specific capacity, providing ideas for the industrial application of sodium ion batteries.

[0078] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A sulfur-doped porous hard carbon material, wherein the particle size D50 of the material is 2 to 15 μm and the mesopore volume is 0.10 to 0.40 cm 3 / g, an average pore diameter of 5 to 35 nm, a pore size range of 0.5 to 100 nm, and a proportion of sulfur element in the sulfur-doped hard carbon material of 0.5wt-5wt%.

2. The sulfur-doped porous hard carbon material according to claim 1, characterized in that: The mesopore volume of the sulfur-doped porous hard carbon material is 0.13 to 0.35 cm 3 / g, average pore diameter 5 to 30nm, pore size range 1.0 to 50nm.

3. The sulfur-doped porous hard carbon material according to claim 1, characterized in that: The mesopore volume of the sulfur-doped porous hard carbon material is 0.17 to 0.26 cm 3 / g, average pore diameter 9.18 to 26.3 nm, pore size range 1.3 to 47.8 nm.

4. The method for preparing the sulfur-doped porous hard carbon material according to claim 1, comprising: 1) Disperse starch in water, add a certain mass of sulfur source and mix, then transfer the mixture to a hydrothermal reactor with a stirring function, first heat it to 70-100°C at 5-10°C / min and keep it warm for 5-20min, control the stirring speed at 500r / min, then heat it to 130-160°C at a heating rate of 5°C / min and keep it warm for 3-6h, and then cool it naturally to room temperature and take it out; 2) adding a certain amount of organic solvent to the sulfur-doped porous starch material treated in step 1) to precipitate the sulfur-doped porous starch, filtering and collecting the sulfur-doped porous starch material after sedimentation, and then vacuum drying to obtain the sulfur-doped porous starch material; 3) The sulfur-doped porous starch obtained in step 2) is used as a precursor to perform high-temperature carbonization calcination under an inert atmosphere. The calcination process is as follows: first, the temperature is increased from room temperature to 200-500°C at 2-20°C / min, and kept warm for 1-5 hours; then the temperature is increased to 1100-1600°C at 1-10°C / min, and kept warm for 1-5 hours; finally, the temperature is naturally cooled to room temperature to obtain a block hard carbon material.

5. The method for preparing sulfur-doped porous hard carbon material according to claim 4, characterized in that: The starch in step 1) includes, but is not limited to, one or more of corn starch, wheat starch, potato starch, tapioca starch, water chestnut starch, and lotus root starch.

6. The method for preparing sulfur-doped porous hard carbon material according to claim 4, characterized in that: The sulfur source in step 1) includes, but is not limited to, one or more of thiourea, ethyl mercaptan, sulfur powder, and sulfur-containing amino acids; preferably, the mass ratio of the sulfur source to starch is 0.1:10 to 5:

10.

7. The method for preparing sulfur-doped porous hard carbon material according to claim 4, characterized in that: The organic solvent used in step 2) includes one or more of ethanol, methanol and propanol.

8. The method for preparing sulfur-doped porous hard carbon material according to claim 4, characterized in that: The inert gas used in step 3) is nitrogen, argon or a mixture of the two.

9. Use of the sulfur-doped porous hard carbon material according to claim 1 as a negative electrode of a sodium ion battery.

10. A sodium ion battery, comprising the sulfur-doped porous hard carbon material according to claim 1 as a negative electrode material.

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