Hollow hard carbon material for negative electrode of sodium-ion battery as well as preparation method and application of hollow hard carbon material

Abstract

The invention belongs to the technical field of sodium-ion battery negative electrode materials, and particularly relates to a sodium-ion battery negative electrode hollow hard carbon material and a preparation method and application thereof. The hard carbon material is provided with a cavity structure and an N-doped coating carbon layer. Silicon dioxide is introduced to serve as a sacrificial template, hard carbon of a cavity structure is formed, and ion transmission is facilitated; an N-doped carbon-coated coating layer is obtained by mixing asphalt and a nitrogen source, high graphitization and few structural defects are achieved, side reaction with an electrolyte is reduced, coulombic efficiency is improved, meanwhile, the nitrogen element is introduced to the surface, the capacity and rate capability of the material are further improved, and the electrochemical performance of the hard carbon material is comprehensively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion battery negative electrode materials, and particularly relates to a hollow hard carbon material for sodium ion battery negative electrodes and a preparation method and application thereof. BACKGROUND

[0002] With the growing demand for sustainable energy storage worldwide, sodium ion batteries are considered as a low-cost energy storage alternative with great potential due to their abundant raw material sodium resources, wide distribution and similar electrochemical characteristics to lithium ion batteries, especially suitable for large-scale energy storage and low-speed electric vehicles. Among the key materials of sodium ion batteries, the choice of negative electrode materials is crucial. Unlike the mature graphite negative electrode in lithium ion batteries, sodium ions are difficult to reversibly intercalate and deintercalate between the layers of graphite, so hard carbon materials with unique pore structure and larger interlayer spacing show more superior application prospects and become one of the most promising sodium ion battery negative electrode materials.

[0003] To improve the electrochemical performance of hard carbon materials, researchers have carried out extensive technical exploration. The current mainstream strategies focus on the regulation of the material itself and the interface, mainly including: optimizing the microstructure (such as porosity, interlayer spacing) and macroscopic morphology of hard carbon by regulating the precursor type and carbonization process; introducing heteroatoms (such as nitrogen, sulfur, phosphorus) for doping to change the electronic structure and electrochemical activity of the material; and building a coating layer (such as carbon layer, polymer-derived carbon) on the surface of hard carbon to stabilize the interface. These methods aim to enhance the diffusion dynamics of sodium ions and improve their interface stability to some extent.

[0004] Although the above strategies have made some progress, hard carbon materials still face significant challenges in practical applications. The rich internal pore structure not only increases the storage sites and diffusion channels of sodium ions, but also leads to a larger specific surface area, thereby increasing the contact area with the electrolyte. This can trigger more severe side reactions during charging and discharging, forming a thick or unstable solid-state electrolyte interface film, which not only consumes a large number of active sodium ions, resulting in a low initial coulombic efficiency, but also affects the long-term stability of the interface, ultimately leading to the difficulty of meeting the commercial requirements of the cycle life and rate performance of the battery. The existing modification methods are often complex or costly, and the fine regulation of pore structure and interface stabilization are still not ideal, so it is of great significance to develop a new type of hollow hard carbon material that can balance high initial coulombic efficiency, excellent cycle stability and high rate performance.

[0005] In addition, on the one hand, due to the difference in understanding of those skilled in the art; on the other hand, because the inventors studied a large number of literatures and patents when making the invention, but limited by the size and did not list all the details and contents in detail, but this does not mean that the invention does not have these prior art characteristics, on the contrary, the invention has all the characteristics of the prior art, and the applicant reserves the right to add relevant prior art in the background art. SUMMARY

[0006] The application belongs to the technical field of sodium ion battery negative electrode materials, and particularly relates to a hollow hard carbon material for sodium ion battery negative electrodes and a preparation method and application thereof.

[0007] In view of the above technical problems, one of the purposes of the present application is to provide a preparation method of a hollow hard carbon material, comprising the following steps: S1: starch is subjected to low-temperature pre-oxidation treatment and then high-temperature carbonization in an inert atmosphere to obtain porous hard carbon microspheres; S2: after the tetraethyl orthosilicate solution reacts completely with the porous hard carbon microspheres in the S1 in an alkaline environment, drying is performed to obtain a spherical hard carbon-SiO2 composite material; S3: after the pitch, nitrogen source powder and the spherical hard carbon-SiO2 composite material in the S2 are uniformly mixed, carbonization is performed in an inert atmosphere to obtain a N-doped carbon-coated spherical hard carbon-SiO2 composite material; S4: washing treatment is performed with hydrofluoric acid.

[0008] According to a preferred embodiment, the starch is one or more of potato starch, corn starch, legume starch, cereal starch and wheat starch.

[0009] According to a preferred embodiment, in the S1, the temperature of the low-temperature pre-oxidation treatment is 180-280 DEG C. Preferably, the temperature of the low-temperature pre-oxidation treatment is 180 DEG C. The temperature of the low-temperature pre-oxidation treatment is 240 DEG C. The temperature of the low-temperature pre-oxidation treatment is 280 DEG C.

[0010] According to a preferred embodiment, in the S1, the holding time of the low-temperature pre-oxidation treatment is 5-24 h. Preferably, the holding time of the low-temperature pre-oxidation treatment is 5 h. The holding time of the low-temperature pre-oxidation treatment is 12 h. The holding time of the low-temperature pre-oxidation treatment is 24 h.

[0011] According to a preferred embodiment, in the S1, the temperature of the high-temperature carbonization is 1000-1500 DEG C. Preferably, the temperature of the high-temperature carbonization is 1000 DEG C. The temperature of the high-temperature carbonization is 1300 DEG C. The temperature of the high-temperature carbonization is 1500 DEG C.

[0012] According to a preferred embodiment, in S1, the holding time of high-temperature carbonization is 2-6 h. Preferably, the holding time of high-temperature carbonization is 2 h. The holding time of high-temperature carbonization is 3 h. The holding time of high-temperature carbonization is 6 h.

[0013] According to a preferred embodiment, in S1, the heating rate of high-temperature carbonization is 1-5℃ / min. Preferably, the heating rate of high-temperature carbonization is 1℃ / min. The heating rate of high-temperature carbonization is 3℃ / min. The heating rate of high-temperature carbonization is 5℃ / min.

[0014] According to a preferred embodiment, in S2, the reaction time of the tetraethyl orthosilicate solution with the porous hard carbon microspheres is 4-12 h. Preferably, the reaction time of the tetraethyl orthosilicate solution with the porous hard carbon microspheres is 4 h. The reaction time of the tetraethyl orthosilicate solution with the porous hard carbon microspheres is 8 h. The reaction time of the tetraethyl orthosilicate solution with the porous hard carbon microspheres is 12 h.

[0015] According to a preferred embodiment, in S2, the concentration of the tetraethyl orthosilicate solution is 0.5-2 mol / L. Preferably, the concentration of the tetraethyl orthosilicate solution is 0.5 mol / L. The concentration of the tetraethyl orthosilicate solution is 1 mol / L. The concentration of the tetraethyl orthosilicate solution is 2 mol / L.

[0016] According to a preferred embodiment, in S2, the pH of the alkaline environment is 10-12. Preferably, the pH of the alkaline environment is 10. The pH of the alkaline environment is 11. The pH of the alkaline environment is 12.

[0017] According to a preferred embodiment, in S2, the drying temperature is 80℃-100℃, and the drying time is 8-24 h. Preferably, the drying temperature is 80℃, and the drying time is 24 h. The drying temperature is 90℃, and the drying time is 12 h. The drying temperature is 100℃, and the drying time is 8 h.

[0018] According to a preferred embodiment, in S2, the molar ratio of tetraethyl orthosilicate to porous hard carbon microspheres is 0.01-0.1. Preferably, the molar ratio of tetraethyl orthosilicate to porous hard carbon microspheres is 0.01. The molar ratio of tetraethyl orthosilicate to porous hard carbon microspheres is 0.05. The molar ratio of tetraethyl orthosilicate to porous hard carbon microspheres is 0.1.

[0019] According to a preferred embodiment, in S3, the pitch is petroleum pitch. Preferably, the pitch is petroleum pitch at 220-280℃.

[0020] According to a preferred embodiment, in S3, the weight of the asphalt is 1-3% of the weight of the material after carbonization (i.e., the spherical hard carbon-SiO2 composite material in S2). Preferably, the weight of the asphalt is 1% of the weight of the material after carbonization. Alternatively, the weight of the asphalt is 2% of the weight of the material after carbonization. Or, the weight of the asphalt is 3% of the weight of the material after carbonization.

[0021] According to a preferred embodiment, in S3, the nitrogen source is one or more of urea, ammonium dihydrogen phosphate, polyacrylonitrile, and chitosan.

[0022] According to a preferred embodiment, in step S3, the weight of the nitrogen source is 2-10% of the weight of the material after the carbonization treatment. Preferably, the weight of the nitrogen source is 2% of the weight of the material after the carbonization treatment. Alternatively, the weight of the nitrogen source is 5% of the weight of the material after the carbonization treatment. Or, the weight of the nitrogen source is 10% of the weight of the material after the carbonization treatment.

[0023] According to a preferred embodiment, in step S3, the carbonization temperature is 800℃-1200℃. Preferably, the carbonization temperature is 800℃. Alternatively, the carbonization temperature may be 1000℃ or 1200℃.

[0024] According to a preferred embodiment, in step S3, the sintering time is 2-6 hours. Preferably, the sintering time is 2 hours. Alternatively, the sintering time is 4 hours. Or, the sintering time is 6 hours.

[0025] According to a preferred embodiment, in S3, the heating rate is 1-5°C / min. Preferably, the heating rate is 1°C / min. Alternatively, the heating rate is 3°C / min. Or, the heating rate is 5°C / min.

[0026] According to a preferred embodiment, in step S4, the concentration of hydrofluoric acid is 0.5-2 mol / L. Preferably, the concentration of hydrofluoric acid is 0.5 mol / L. Alternatively, the concentration may be 1 mol / L or 2 mol / L.

[0027] According to a preferred embodiment, in S3, the inert gas is at least one of nitrogen or argon.

[0028] One of the objectives of this invention is to provide hollow hard carbon materials prepared by the above-described preparation method. The hollow hard carbon material is a nitrogen-doped carbon-coated material with a cavity structure.

[0029] One object of this invention is to provide the application of the hollow hard carbon material prepared by the above-described method in the preparation of sodium-ion batteries. Preferably, the hollow hard carbon material is used in the preparation of the negative electrode of a sodium-ion battery. More preferably, the hollow hard carbon material is used in the preparation of the negative electrode sheet of a sodium-ion battery.

[0030] The beneficial effects of this invention are: This invention successfully constructed a hard carbon material with a unique hollow structure by using silica as a sacrificial template. This structure significantly improves the material's internal porosity and specific surface area, providing abundant diffusion channels and sufficient active sites for the rapid migration and efficient storage of sodium ions. This significantly enhances the rate performance of the anode material, enabling it to maintain excellent capacity even at high current densities.

[0031] Furthermore, by mixing and simultaneously carbonizing bitumen with a nitrogen source precursor, a uniform nitrogen-doped carbon coating layer was formed in situ on the hard carbon surface. This coating layer exhibits a high degree of graphitization and good electronic conductivity, while effectively reducing structural defects on the carbon material surface. This design not only constructs a stable interfacial protective layer, significantly reducing side reactions between the hard carbon material and the electrolyte and effectively suppressing the formation of excess solid electrolyte interfacial film, thereby significantly improving the initial coulombic efficiency of the material; but also, the nitrogen element introduced on the surface acts as an active site, further enhancing the adsorption capacity of sodium ions and contributing additional pseudocapacitance, achieving a simultaneous improvement in the material's capacity and rate performance.

[0032] Specifically, the material in the example exhibits a higher initial discharge specific capacity (361.69 mAh / g) and lower irreversible capacity loss, resulting in an excellent initial coulombic efficiency (first-time efficiency) of 92.49%, significantly higher than the comparative example. This data directly confirms the key role of the nitrogen-doped carbon coating layer on the surface: its high degree of graphitization and complete structure effectively reduce the contact between carbon material surface defects and the electrolyte, suppress the occurrence of side reactions, and reduce sodium ion consumption during the formation of the solid electrolyte interphase (SEI) film, thereby significantly improving energy efficiency.

[0033] Meanwhile, the voltage-specific capacitance curves shown in the examples further confirm the comprehensive advantages of the material. The curves indicate that the material not only possesses a high reversible specific capacity, but also a smoother charge-discharge plateau with less polarization. This result is attributed to the synergistic effect of the hollow structure and nitrogen doping: the unique hollow cavity provides a channel for the rapid transport of sodium ions, enhancing rate performance; while the introduction of nitrogen provides additional active sites, enhancing the contribution of pseudocapacitance, together ensuring the material's rapid response kinetics at high capacities.

[0034] In summary, the synergistic effect of the hollow structure and surface nitrogen-doped carbon coating of this invention optimizes the physical and electrochemical properties of the material from the bulk phase to the interface, and together achieves a comprehensive improvement in the initial coulombic efficiency, reversible capacity, rate performance and long-term cycle stability of hard carbon anode materials, providing a highly efficient and integrated solution to overcome the technical bottlenecks of existing hard carbon materials. Attached Figure Description

[0035] Figure 1 This is a comparison chart of the charge-discharge curves of the hollow hard carbon materials of Example 1 and Comparative Example 1 under 0.1 C conditions. Detailed Implementation

[0036] In the description of this invention, terminology is used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0037] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials, reagents or instruments used, unless otherwise specified by the manufacturer, are all commercially available reagents and materials; the conditions not specified in the examples are all carried out according to conventional conditions or conditions recommended by the manufacturer. At the same time, the present invention does not limit the source of the raw materials used. Unless otherwise specified, the raw materials used in the present invention are all commercially available products in this technical field.

[0038] Example 1 (1) Place corn starch in a carbonization furnace and heat it to 240°C at a heating rate of 3°C / min under an air atmosphere. Hold it for 12 h to obtain the first precursor. After grinding, heat it to 1300°C at a heating rate of 5°C / min under a nitrogen atmosphere and hold it for 3 h. After cooling to room temperature, porous hard carbon microspheres can be obtained.

[0039] (2) Take 1.2 g of the porous hard carbon microspheres from step (1) and add them to 50 mL of ethanol and 10 mL of water. After ultrasonic dispersion, add 2 mL of 25% ammonia water (to make the solution pH 10), and then add 30 mL of tetraethyl orthosilicate solution (1 mol / L). Stir at 700 r / min at 25℃ for 12 h. Finally, heat and evaporate the solvent at 60℃ in a rotary evaporator to obtain spherical hard carbon-SiO2 composite material.

[0040] (3) 10 g of the spherical hard carbon-SiO2 composite material from step (2) was mixed with 0.2 g of asphalt and 0.5 g of ammonium dihydrogen phosphate powder in a ball mill. The ball milling speed was 300 r / min and the ball milling time was 0.5 h to obtain the precursor powder. The precursor powder was sintered in a nitrogen atmosphere. The heating rate was 1℃ / min, the sintering temperature was 1000℃, and the sintering time was 2 h. The obtained product was washed with hydrofluoric acid (2 mol / L) to obtain a hard carbon material with a cavity structure and N-doped carbon coating.

[0041] Example 2 This embodiment proposes a cavity-structured N-doped carbon-coated hard carbon material, which is prepared in the same way as in Example 1, except that in step (2), “add 30 mL of ethyl silicate solution (1 mol / L)” is changed to “add 10 mL of ethyl silicate solution (1.5 mol / L)”.

[0042] Example 3 This embodiment proposes a cavity-structured N-doped carbon-coated hard carbon material, which is prepared in the same way as in Example 1, except that "0.2 g asphalt and 0.5 g ammonium dihydrogen phosphate powder" in step (3) is changed to "0.1 g asphalt and 0.8 g urea powder".

[0043] Example 4 (1) Place corn starch in a carbonization furnace and heat it to 280°C at a heating rate of 5°C / min under an air atmosphere. Hold it for 24 h to obtain the first precursor. After grinding, heat it to 1500°C at a heating rate of 5°C / min under a nitrogen atmosphere and hold it for 2 h. After cooling to room temperature, porous hard carbon microspheres can be obtained.

[0044] (2) Take 1.2 g of the porous hard carbon microspheres from step (1) and add them to 50 mL of ethanol and 10 mL of water. After ultrasonic dispersion, add 2.5 mL of 25% ammonia water (to make the solution pH 12), and then add 32 mL of tetraethyl orthosilicate solution (2 mol / L). Stir at 900 r / min for 4 h at 25℃. Finally, heat and evaporate the solvent at 60℃ in a rotary evaporator to obtain spherical hard carbon-SiO2 composite material.

[0045] (3) 10 g of the spherical hard carbon-SiO2 composite material from step (2) was mixed with 0.3 g of asphalt and 0.5 g of ammonium dihydrogen phosphate powder in a ball mill. The ball milling speed was 200 r / min and the ball milling time was 1 h to obtain the precursor powder. The precursor powder was sintered in a nitrogen atmosphere. The heating rate was 5℃ / min, the sintering temperature was 1200℃, and the sintering time was 6 h. The obtained product was washed with hydrofluoric acid (0.5 mol / L) to obtain a hard carbon material with a cavity structure and N-doped carbon coating.

[0046] Comparative Example 1 This comparative example presents a porous hard carbon, which is prepared in the same way as in Example 1, except that steps (2) and (3) are removed.

[0047] Comparative Example 2 This comparative example presents a hard carbon material, which is prepared in the same way as in Example 1, except that step (3) is removed.

[0048] Test case Sodium-ion batteries were fabricated using the negative electrode materials prepared in the above embodiments and comparative examples, and the electrochemical performance of each battery was tested. For the electrochemical performance test, the negative electrode materials prepared in the above embodiments and comparative examples were mixed in a mass ratio of 95:2:1.5:1.5 (negative electrode material: styrene-butadiene rubber: sodium carboxymethyl cellulose: conductive carbon black), and a negative electrode slurry was prepared using deionized water as a solvent. The negative electrode slurry was then coated onto aluminum foil, vacuum dried at 100°C, and rolled to obtain the negative electrode sheet. The negative electrode sheet, the counter electrode sheet (metallic sodium), the electrolyte (1 mol / L NaPF6 dissolved in a 1:1 mass ratio mixture of ethylene carbonate (EC) and diethyl carbonate (DEC)), and the glass fiber separator were then assembled into a coin cell. The coin cell was subjected to one discharge-charge cycle on a battery tester. The charge-discharge rate was 0.1 C, and the voltage range was 0.001-2.5 V. The test results are shown in Table 1.

[0049] Table 1 shows the electrochemical performance of the hard carbon anode materials in Examples 1-3 and Comparative Examples 1-2 in coin cells.

[0050] Table 1

[0051] Figure 1 This is a comparison of the charge-discharge curves of the hard carbon anode materials of Example 1 and Comparative Example 1 at 0.1 C. At 0.1 C, the hard carbon anode material of Comparative Example 1 exhibits a reversible capacity of 294.81 mAh / g and an initial coulombic efficiency of 87.73%, while the hard carbon anode material of Example 1 achieves a reversible capacity of 334.54 mAh / g and an initial coulombic efficiency of 92.49%. Based on the data in Table 1, the charge specific capacity and initial efficiency of the present application's examples are higher than those of the comparative example's hard carbon material. These results demonstrate that the hard carbon prepared in this application possesses unique structural characteristics, providing a high-quality and efficient ion channel for ion transport. Simultaneously, the nitrogen-doped carbon coating layer exhibits high graphitization and fewer structural defects, reducing side reactions with the electrolyte, improving coulombic efficiency and specific capacity, and comprehensively enhancing the electrochemical performance of the hard carbon material.

[0052] It should be noted that the specific embodiments described above are exemplary, and those skilled in the art can devise various solutions inspired by the disclosure of this invention. These solutions all fall within the scope of this invention and its protection. Those skilled in the art should understand that this specification and its accompanying drawings are illustrative and not intended to limit the scope of the claims. The scope of protection of this invention is defined by the claims and their equivalents.

Claims

1. A method for preparing a hollow hard carbon material, characterized in that, Includes the following steps: S1: After low-temperature pre-oxidation treatment of starch, high-temperature carbonization is carried out in an inert atmosphere to obtain porous hard carbon microspheres. S2: After the tetraethyl orthosilicate solution reacts completely with the porous hard carbon microspheres in S1 under alkaline conditions, it is dried to obtain a spherical hard carbon-SiO2 composite material. S3: After uniformly mixing asphalt, nitrogen source powder and the spherical hard carbon-SiO2 composite material in S2, carbonize in an inert atmosphere to obtain a nitrogen-doped carbon-coated spherical hard carbon-SiO2 composite material. S4: Wash with hydrofluoric acid.

2. The preparation method according to claim 1, characterized in that, The starch is one or more of potato starch, corn starch, bean starch, cereal starch, and wheat starch.

3. The preparation method according to claim 1, characterized in that, In S1, the temperature of the low-temperature pre-oxidation treatment is 180℃-280℃.

4. The preparation method according to claim 1, characterized in that, In S1, the high-temperature carbonization temperature is 1000-1500℃.

5. The preparation method according to claim 1, characterized in that, In S2, the concentration of the tetraethyl orthosilicate solution is 0.5-2 mol / L.

6. The preparation method according to claim 1, characterized in that, In S2, the molar ratio of tetraethyl orthosilicate to porous hard carbon microspheres is 0.01-0.

1.

7. The preparation method according to claim 1, characterized in that, In S3, the asphalt is petroleum asphalt.

8. The preparation method according to claim 1, characterized in that, In S3, the weight of the asphalt is 1-3% of the weight of the material after carbonization treatment.

9. The hollow hard carbon material according to any one of claims 1-8, characterized in that, The hollow hard carbon material is a nitrogen-doped carbon-coated material with a cavity structure.

10. The application of the hollow hard carbon material prepared by any one of the preparation methods of claims 1-8 in the preparation of sodium-ion batteries.

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