A spherical sulfurized polyacrylonitrile-based hard carbon negative electrode material, a preparation method and application thereof

Abstract

The application discloses a kind of spherical sulfurized polyacrylonitrile-based hard carbon negative materials and preparation method and application thereof, and it is related to sodium ion negative material preparation technical field.The preparation method of the application includes: first, polyacrylonitrile and sulfur sublimate are added into ball mill jar in certain proportion and ball milled, then dried, finally placed in the tube furnace with inert atmosphere protection and carried out two-step heat treatment, finally obtain hard carbon negative material, the application also provides the application of the hard carbon negative material in the preparation of sodium ion battery.The application aims to prepare S-doped polyacrylonitrile-derived hard carbon material by sulfurizing treatment of polyacrylonitrile and sulfur sublimate, and then carbonizing at high temperature (>1200 DEG C).The preparation method provided by the application is simple, easy to operate, and the raw material carbon yield is high.The hard carbon negative electrode is prepared by ball milling and two-step heat preservation method, and has the advantages of high initial coulomb efficiency, good cycle performance and high rate performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium ion anode material preparation technology, specifically relating to a spherical vulcanized polyacrylonitrile-based hard carbon anode material, its preparation method, and its application. Background Technology

[0002] Polyacrylonitrile (PAN), as an important synthetic precursor, has attracted much attention in the field of carbon material preparation due to its high carbon yield, excellent spinnability, and the ability to easily form disordered graphite structures through heat treatment. In recent years, with the rise of sodium-ion batteries as a potential alternative to lithium-ion batteries in large-scale energy storage, the development of high-performance, low-cost anode materials has become a key research focus. Hard carbon materials derived from PAN pyrolysis, with their abundant defect sites, moderate interlayer spacing, and excellent sodium storage platform capacity, are considered one of the most promising anode materials for sodium-ion batteries. However, the specific capacity, first coulombic efficiency, and rate performance of traditional PAN-based hard carbon still need further improvement, and the optimization of its electrochemical performance is closely related to the precise control of its microstructure (such as interlayer spacing, defect concentration, and electronic conductivity).

[0003] To optimize the electrochemical performance of hard carbon anodes, elemental doping has proven to be an effective modification strategy. By introducing heteroatoms (such as N, S, P, and B) into the carbon framework, the electronic structure of carbon materials can be effectively tuned, the interlayer spacing expanded, and more active defect sites introduced, thereby enhancing the adsorption and diffusion kinetics of sodium ions. Among these, sulfur (S) atoms exhibit unique advantages in carbon material doping modification due to their large atomic radius and the significant electronic effects resulting from covalent bonding with carbon atoms. S doping not only expands the interlayer spacing and alleviates the volumetric strain during sodium ion insertion / extraction, but its lone pair electrons can also increase the charge density of the carbon matrix, improve electronic conductivity, and potentially introduce additional pseudocapacitive contributions to sodium storage. Therefore, introducing S atoms into the PAN-based hard carbon framework is expected to synergistically improve its sodium storage performance from multiple dimensions.

[0004] Currently, sulfurized polyacrylonitrile (SPAN) and its composites have been preliminarily explored in the field of energy storage, especially in lithium-sulfur battery systems. SPAN materials that undergo low-temperature pyrolysis (typically below 400 °C) have been widely studied due to their effective sulfur fixation and suppression of polysulfide shuttle. Some literature also discloses the use of sulfurized polyacrylonitrile as a cathode to prepare sulfur-based sodium-ion batteries, such as Chinese patent CN 120878942 A. This patent utilizes the significantly higher specific capacity of the SPAN cathode compared to traditional sodium-ion cathodes to match a hard carbon anode, overcoming the bottlenecks of traditional sodium-ion batteries in terms of energy density, cycle life, safety, and cost through complementary and synergistic material properties. However, research on applying this system to hard carbon anodes in sodium-ion batteries is relatively limited, and the focus is mostly on medium-temperature carbonization products. Carbonizing SPAN precursors at higher temperatures (e.g., above 1300 °C) to obtain highly stable, structurally ordered sulfur-doped hard carbon, and systematically studying its performance and structure-property relationship as a sodium-ion anode, is a valuable but not yet fully explored research direction. Summary of the Invention

[0005] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide a spherical vulcanized polyacrylonitrile-based hard carbon anode material, its preparation method and application.

[0006] To address the aforementioned technical problems, this invention aims to prepare S-doped polyacrylonitrile-derived hard carbon materials by sulfiding polyacrylonitrile with sublimed sulfur and then carbonizing it at a high temperature (1200 °C). This invention systematically characterizes the microstructure, surface chemical state, and sulfur presence forms of this material, elucidating the influence of S-doped hard carbon on interlayer spacing, defect types, electronic conductivity, and surface chemistry. The prepared S-doped polyacrylonitrile-derived hard carbon material is then used as an anode material for sodium-ion batteries, comprehensively evaluating its specific capacity, cycle stability, rate performance, and initial coulombic efficiency, among other key electrochemical indicators. Furthermore, kinetic analysis is used to explore the contribution of S doping to the sodium storage mechanism. Unlike existing technologies that use sulfided polyacrylonitrile as the cathode in sulfur-based sodium-ion batteries, this invention uses S-doped polyacrylonitrile-derived hard carbon materials as the anode in sodium-ion battery preparation. Currently, sulfided polyacrylonitrile (SPAN) and its composites have been preliminarily explored in the field of energy storage, especially in lithium-sulfur battery systems. SPAN materials that undergo low-temperature pyrolysis (typically below 400 °C) have been widely studied due to their effective sulfur fixation and suppression of polysulfide shuttle. However, research on applying this system to hard carbon anodes in sodium-ion batteries is relatively limited, and most attention has been focused on carbonization products at moderate temperatures. Carbonizing the SPAN precursor at higher temperatures (e.g., above 1300 °C) to obtain highly stable, structurally ordered S-doped hard carbon, and systematically studying its performance and structure-property relationship as a sodium-ion battery anode, is a valuable but not yet fully explored research direction. This invention not only provides a new precursor design and modification approach for developing high-performance hard carbon anodes for sodium-ion batteries, but also provides experimental evidence for a deeper understanding of the stable existence forms of high-temperature S doping in carbon materials and its electrochemical mechanisms.

[0007] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a spherical vulcanized polyacrylonitrile-based hard carbon anode material, comprising the following steps: S1. Mix and ball-mill the polyacrylonitrile and sublimed sulfur, and then dry the slurry after ball milling; S2. The dried powder is kept at 300~400℃ for 6~14h under an inert atmosphere, cooled and taken out to obtain vulcanized polyacrylonitrile. S3. The vulcanized polyacrylonitrile is kept at 1200~1400℃ for 1~3h under an inert atmosphere, cooled and taken out to obtain spherical vulcanized polyacrylonitrile-based hard carbon material.

[0008] Optionally, in S1, polyacrylonitrile, sublimed sulfur and dispersant are added to a ball mill jar for ball milling. The ball milling speed is 600 r / min to 800 r / min, and the ball milling time is 2 to 4 hours. The dispersant is anhydrous ethanol.

[0009] Optionally, in S1, the mass ratio of polyacrylonitrile to sublimed sulfur is 1.5~2.5:1.

[0010] Optionally, in S2, the dried powder is kept at 350°C for 10 hours under an inert atmosphere.

[0011] Optionally, in step S3, the vulcanized polyacrylonitrile is kept at 1300°C for 1.5 hours under an inert atmosphere.

[0012] Optionally, in S2 and S3, the inert atmosphere is nitrogen or argon.

[0013] Secondly, the present invention provides a spherical vulcanized polyacrylonitrile-based hard carbon anode material, which is obtained by the preparation method described above.

[0014] Thirdly, the present invention provides a battery negative electrode sheet made from the aforementioned spherical vulcanized polyacrylonitrile-based hard carbon negative electrode material.

[0015] Optionally, the method for preparing the battery negative electrode sheet includes the following steps: The spherical vulcanized polyacrylonitrile-based hard carbon anode material, conductive agent, binder and solvent are mixed and coated on a metal substrate, and then vacuum dried to obtain the battery anode sheet.

[0016] Fourthly, the present invention provides the application of the spherical vulcanized polyacrylonitrile-based hard carbon anode material or the battery anode sheet in the preparation of sodium-ion batteries.

[0017] Fifthly, the present invention provides a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is a metallic sodium sheet, and the negative electrode is a negative electrode sheet prepared from the spherical sulfurized polyacrylonitrile-based hard carbon negative electrode material or the negative electrode sheet of the battery.

[0018] This invention has at least one of the following beneficial effects: (1) The preparation method provided by the present invention is simple, easy to operate, and has a high carbon yield. The present invention prepares a hard carbon anode by ball milling and two-step heat preservation, which has the advantages of high initial coulombic efficiency, good cycle performance and high rate performance, and excellent sodium storage performance.

[0019] (2) Compared with undoped hard carbon anode materials, the S doping of the present invention with a larger radius increases the interlayer spacing of carbon microcrystals and reduces the steric hindrance of sodium ion intercalation; the rich closed-pore structure provides additional sodium storage space for sodium ion filling. Attached Figure Description

[0020] Figure 1The images shown are SEM images of sample 1300-SPAN-2 at (a) 3000 and (b) 1000 magnification, and (c) SEM images of sample 1300-SPAN-1.5 and (d) SEM images of sample 1300-SPAN-2.5 at 1000 magnification.

[0021] Figure 2 The image shows samples 1200-PAN, 1300-PAN, and 1400-PAN at 15 mA g. -1 The first charge-discharge curve at current density.

[0022] Figure 3 The images show samples 1300-PAN, 1300-SPAN-1.5, 1300-SPAN-2, and 1300-SPAN-2.5 at 15 mAg. -1 The first charge-discharge curve at current density.

[0023] Figure 4 The image shows samples 1300-PAN, 1300-SPAN-1.5, 1300-SPAN-2, and 1300-SPAN-2.5 at 150 mA g. -1 Cyclic curves at current density.

[0024] Figure 5 The figures show samples 1300-PAN, 1300-SPAN-1.5, 1300-SPAN-2, and 1300-SPAN-2.5 at concentrations of 30, 60, 90, 150, 300, 600, 900, and 30 mA g, respectively. -1 Ratio curves at current density. Detailed Implementation

[0025] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0026] The polyacrylonitrile used in the following examples and comparative examples was produced by Shanghai Maclean Biochemical, with analytical grade and molecular weight of 150,000.

[0027] The sublimed sulfur used in the following examples and comparative examples was produced by Sinopharm Chemical Reagent Co., Ltd., and was of analytical grade.

[0028] Example 1 This embodiment uses polyacrylonitrile as a raw material to prepare hard carbon anode material, and then uses the prepared hard carbon anode material to prepare sodium-ion batteries to explore the optimal reaction temperature of polyacrylonitrile under an inert atmosphere. The specific method is as follows: Preparation method of hard carbon anode material: Polyacrylonitrile (-[CH2–CH(CN)]-) was heated at 1200℃, 1300℃ and 1400℃ for 2h under argon atmosphere to obtain three kinds of hard carbon anode materials, named 1200-PAN, 1300-PAN and 1400-PAN respectively.

[0029] The three types of hard carbon anode materials prepared above were used to prepare sodium-ion batteries, and the specific methods are as follows: A button cell battery, the preparation method of which includes the following steps: The three types of hard carbon anode materials prepared above were mixed with super-p conductive agent and polyvinylidene fluoride binder at a mass ratio of 8:1:1, and 20 mL of N-methyl-2-pyrrolidone was added to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into circular electrode sheets and vacuum-dried at 120 °C for 12 h. Using the prepared hard carbon as the positive electrode, sodium metal sheet as the negative electrode, 1 M NaCF3SO3 in DIGLYME = 100 Vol% as the electrolyte, and a glass fiber separator, 2032 type button cells were assembled in a glove box. Cycle and rate performance tests were conducted on the button cells using a Newway battery tester (room temperature, voltage range 0.001-2 V vs. Na / Na). + ).

[0030] The result is as follows Figure 2 As shown in Table 1, the test results indicate that the hard carbon anode material 1200-PAN can achieve a current density of 15 mA·g. -1 At that time, the initial specific capacity was 169.94 mAh·g. -1 The initial coulombic efficiency was 79.50%. The hard carbon anode material 1300-PAN achieved a current density of 15 mA·g. -1 At that time, the initial specific capacity was 171.63 mAh·g. -1 The initial coulombic efficiency was 77.83%; the hard carbon anode material 1400-PAN achieved a current density of 15 mA·g. -1 At that time, the initial specific capacity was 134.01 mAh·g. -1 The initial Coulomb efficiency was 64.61%. The electrochemical performance of the sodium-ion battery hard carbon anode material prepared in Example 1 is compared in Table 1.

[0031] Table 1 Comparison of Electrochemical Performance of Materials Among them, 1300-PAN showed the best overall capacity performance. Therefore, subsequent experiments were conducted by holding the vulcanized polyacrylonitrile at 1300℃ under an argon atmosphere and exploring the optimal holding time.

[0032] Example 2 A method for preparing a spherical vulcanized polyacrylonitrile-based hard carbon anode material specifically includes the following steps: Polyacrylonitrile and sublimed sulfur were added to a ball mill jar at a mass ratio of 1.5:1 and mixed in the liquid phase at 700 r / min for 3 h. Anhydrous ethanol was used as the dispersant, and the ratio of polyacrylonitrile to dispersant was 1.5 g: 20 mL. The ball-milled slurry was then dried in a 60 °C forced-air drying oven. The dried powder was placed in a tube furnace and held at 350 °C for 10 h under an inert atmosphere. After natural cooling, it was removed to obtain vulcanized polyacrylonitrile. The vulcanized polyacrylonitrile was placed in a high-temperature tube furnace at 1300 °C and held at an inert atmosphere for 2 h. After natural cooling, it was removed to obtain a hard carbon anode material (named 1300-SPAN-1.5).

[0033] The morphology of the prepared hard carbon anode material 1300-SPAN-1.5 was characterized, such as... Figure 1 Figure c shows the SEM image of the hard carbon anode material 1300-SPAN-1.5 at a magnification of 1000. It can be seen that the hard carbon anode material prepared in this embodiment is spherical or approximately spherical.

[0034] The hard carbon anode material 1300-SPAN-1.5 prepared above was used to prepare sodium-ion batteries. The specific method is as follows: A button cell battery, the preparation method of which includes the following steps: The prepared hard carbon anode material 1300-SPAN-1.5, super-p conductive agent, and polyvinylidene fluoride binder were mixed with 20 mL of N-methyl-2-pyrrolidone at a mass ratio of 8:1:1 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into circular electrode sheets and vacuum-dried at 120 °C for 12 h. Using the prepared hard carbon as the positive electrode, sodium metal as the negative electrode, 1 M NaCF3SO3 in DIGLYME = 100 Vol% as the electrolyte, and a glass fiber separator, a 2032 type button cell was assembled in a glove box. Cycle and rate performance tests were conducted on the button cell using a Newway battery tester (room temperature, voltage range 0.001-2V vs. Na / Na). + ).

[0035] The result is as follows Figures 3-5 As shown in Table 2, the test results indicate that the hard carbon anode material 1300-SPAN-1.5 achieves a current density of 15 mA·g. -1 At that time, the initial specific capacity was 294.49 mAh·g. -1 The initial Coulomb efficiency was 86.22%.

[0036] Example 3 A method for preparing a spherical vulcanized polyacrylonitrile-based hard carbon anode material specifically includes the following steps: Polyacrylonitrile and sublimed sulfur were added to a ball mill jar at a mass ratio of 2:1 and mixed in the liquid phase at 700 r / min for 3 h. Anhydrous ethanol was used as the dispersant, and the ratio of polyacrylonitrile to dispersant was 2 g: 20 mL. The ball-milled slurry was then dried in a 60℃ forced-air drying oven. The dried powder was placed in a tube furnace and held at 350℃ for 10 h under an inert atmosphere. After natural cooling, it was removed to obtain vulcanized polyacrylonitrile. The vulcanized polyacrylonitrile was placed in a high-temperature tube furnace at 1300℃ and held at an inert atmosphere for 2 h. After natural cooling, it was removed to obtain a hard carbon anode material (named 1300-SPAN-2).

[0037] The morphology of the prepared hard carbon anode material 1300-SPAN-2 was characterized, such as... Figure 1 a and Figure 1 Figure b shows SEM images of hard carbon material 1300-SPAN-2 at magnifications of 3000 and 1000. It can be seen that the hard carbon anode material prepared in this embodiment is spherical or approximately spherical.

[0038] The hard carbon anode material 1300-SPAN-2 prepared above was used to prepare a sodium-ion battery. The specific method is as follows: A button cell battery, the preparation method of which includes the following steps: The prepared hard carbon anode material 1300-SPAN-2, super-p conductive agent, and polyvinylidene fluoride binder were mixed with N-methyl-2-pyrrolidone at a mass ratio of 8:1:1 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into circular electrode sheets and vacuum-dried at 120 °C for 12 h. Using the prepared hard carbon as the positive electrode, a sodium metal sheet as the negative electrode, 1M NaCF3SO3 in DIGLYME = 100 Vol% as the electrolyte, and a glass fiber separator, a 2032 type button cell was assembled in a glove box. Cycle and rate performance tests were conducted on the button cell using a Newway battery tester (room temperature, voltage range 0.001-2V vs. Na / Na). + ).

[0039] The result is as follows Figures 3-5 As shown in Table 2, the test results indicate that the hard carbon anode material 1300-SPAN-2 can achieve a current density of 15 mA·g. -1 At that time, the initial specific capacity was 305.22 mAh·g. -1 The initial Coulomb efficiency was 81.81%.

[0040] Example 4 A method for preparing a spherical vulcanized polyacrylonitrile-based hard carbon anode material specifically includes the following steps: Step 1: Polyacrylonitrile and sublimed sulfur were added to a ball mill jar at a mass ratio of 2.5:1 and mixed in the liquid phase at 700 r / min for 3 h. Anhydrous ethanol was used as the dispersant, and the ratio of polyacrylonitrile to dispersant was 2.5 g: 20 mL. The ball-milled slurry was then dried in a 60℃ forced-air drying oven. The dried powder was placed in a tube furnace and held at 350℃ for 10 h under an inert atmosphere. After natural cooling, it was removed to obtain vulcanized polyacrylonitrile. The vulcanized polyacrylonitrile was placed in a high-temperature tube furnace at 1300℃ and held at an inert atmosphere for 2 h. After natural cooling, it was removed to obtain a hard carbon anode material (named 1300-SPAN-2.5).

[0041] The morphology of the prepared hard carbon anode material 1300-SPAN-2.5 was characterized, such as... Figure 1 Figure d shows the SEM image of the hard carbon anode material 1300-SPAN-2.5 at a magnification of 1000. It can be seen that the hard carbon anode material prepared in this embodiment is spherical or approximately spherical.

[0042] The hard carbon anode material 1300-SPAN-2.5 prepared above was used to prepare sodium-ion batteries. The specific method is as follows: A button cell battery, the preparation method of which includes the following steps: The prepared hard carbon anode material 1300-SPAN-2.5, super-p conductive agent, and polyvinylidene fluoride binder were mixed with N-methyl-2-pyrrolidone at a mass ratio of 8:1:1 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into circular electrode sheets and vacuum-dried at 120 °C for 12 h. Using the prepared hard carbon as the positive electrode, a sodium metal sheet as the negative electrode, 1M NaCF3SO3 in DIGLYME = 100 Vol% as the electrolyte, and a glass fiber separator, a 2032 type button cell was assembled in a glove box. Cycle and rate performance tests were conducted on the button cell using a Newway battery tester (room temperature, voltage range 0.001-2V vs. Na / Na). + ).

[0043] The result is as follows Figures 3-5 As shown in Table 2, the test results indicate that the hard carbon anode material 1300-SPAN-2.5 performs well at a current density of 15 mA·g. -1 At that time, the initial specific capacity was 303.31 mAh·g. -1 The initial Coulomb efficiency was 82.23%. The electrochemical performance of the sodium-ion battery hard carbon anode materials prepared in Examples 2-4 above is compared in Table 2.

[0044] Table 2 Comparison of Electrochemical Performance of Materials As shown in the table above, the reversible specific capacity and ICE of the materials were significantly improved after S doping. The ICE of the samples increased to 86.22% of 1300-SPAN-1.5, 81.81% of 300-SPAN-2, and 82.32% of 1300-SPAN-2.5. Therefore, when the mass ratio of polyacrylonitrile to sublimed sulfur is 1.5:1, 2:1, and 2.5:1, the materials all exhibit good reversible specific capacity and ICE.

[0045] Example 5 A method for preparing a spherical vulcanized polyacrylonitrile-based hard carbon anode material specifically includes the following steps: Polyacrylonitrile and sublimed sulfur were added to a ball mill jar at a mass ratio of 1.5:1 and mixed in the liquid phase at 700 r / min for 3 h. Anhydrous ethanol was used as the dispersant, and the ratio of polyacrylonitrile to dispersant was 1.5 g: 20 mL. The ball-milled slurry was then dried in a 60 °C forced-air drying oven. The dried powder was placed in a tube furnace and held at 350 °C for 10 h under an inert atmosphere. After natural cooling, it was removed to obtain vulcanized polyacrylonitrile. The vulcanized polyacrylonitrile was placed in a high-temperature tube furnace at 1300 °C and held at an inert atmosphere for 0.5 h, 1 h, 2 h, and 4 h, respectively. After natural cooling, it was removed to obtain hard carbon anode materials (named 1300-SPAN-0.5 h, 1300-SPAN-1 h, 1300-SPAN-2 h, and 1300-SPAN-4 h, respectively).

[0046] The hard carbon anode materials 1300-SPAN-0.5h, 1300-SPAN-1h, 1300-SPAN-2h, and 1300-SPAN-4h prepared above were used to prepare sodium-ion batteries. The specific method is as follows: A button cell battery, the preparation method of which includes the following steps: The prepared hard carbon anode materials 1300-SPAN-0.5h, 1300-SPAN-1h, 1300-SPAN-2h, and 1300-SPAN-4h were mixed with super-p conductive agent and polyvinylidene fluoride binder at a mass ratio of 8:1:1, and 20 mL of N-methyl-2-pyrrolidone was added to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into circular electrode sheets and vacuum-dried at 120 °C for 12 h. Using the prepared hard carbon as the positive electrode, a sodium metal sheet as the negative electrode, 1 M NaCF3SO3 in DIGLYME = 100 vol% as the electrolyte, and a glass fiber separator, 2032 type button cells were assembled in a glove box. Cycle and rate performance tests were conducted on the button cells using a Newway battery tester (room temperature, voltage range 0.001-2 V vs. Na / Na+).

[0047] The results are shown in Table 3.

[0048] Table 3 Comparison of Electrochemical Performance of Materials As shown in the table above, the material held in a high-temperature furnace for 2 hours has good reversible specific capacity and ICE.

[0049] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a spherical vulcanized polyacrylonitrile-based hard carbon anode material, characterized in that, Includes the following steps: S1. Mix and ball-mill the polyacrylonitrile and sublimed sulfur, and then dry the slurry after ball milling; S2. The dried powder is kept at 300~400℃ for 6~14h under an inert atmosphere, cooled and taken out to obtain vulcanized polyacrylonitrile. S3. The vulcanized polyacrylonitrile is kept at 1200~1400℃ for 1~3h under an inert atmosphere, cooled and taken out to obtain spherical vulcanized polyacrylonitrile-based hard carbon material.

2. The preparation method according to claim 1, characterized in that, In step S1, polyacrylonitrile, sublimed sulfur, and a dispersant are added to a ball mill jar for ball milling. The ball milling speed is 600 r / min to 800 r / min, and the ball milling time is 2 to 4 hours. The dispersant is anhydrous ethanol.

3. The preparation method according to claim 1, characterized in that, In S1, the mass ratio of polyacrylonitrile to sublimed sulfur is 1.5~2.5:

1.

4. The preparation method according to claim 1, characterized in that, In S2, the dried powder is kept at 350°C for 10 hours under an inert atmosphere.

5. The preparation method according to claim 1, characterized in that, In step S3, the vulcanized polyacrylonitrile is kept at 1300°C for 1.5 hours under an inert atmosphere.

6. A spherical vulcanized polyacrylonitrile-based hard carbon anode material, characterized in that, It is obtained by the preparation method described in any one of claims 1 to 5.

7. A battery negative electrode sheet, characterized in that, It is prepared from the spherical vulcanized polyacrylonitrile-based hard carbon anode material as described in claim 6.

8. The battery negative electrode sheet according to claim 7, characterized in that, The method for preparing the negative electrode sheet of the battery includes the following steps: The spherical vulcanized polyacrylonitrile-based hard carbon anode material, conductive agent, binder and solvent are mixed and coated on a metal substrate, and then vacuum dried to obtain the battery anode sheet.

9. The application of the spherical vulcanized polyacrylonitrile-based hard carbon anode material of claim 6 or the battery anode sheet of claim 7 in the preparation of sodium-ion batteries.

10. A sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The positive electrode is a sodium metal sheet, and the negative electrode is a negative electrode sheet prepared from the spherical vulcanized polyacrylonitrile-based hard carbon negative electrode material of claim 6 or the battery negative electrode sheet of claim 7.

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