Sodium ion battery hard carbon negative electrode material based on step-by-step synergistic regulation and preparation method thereof

Abstract

The application discloses a preparation method of a sodium ion battery hard carbon negative electrode material based on step-by-step synergistic regulation, and comprises the following steps: S1, biomass pretreatment; S2, low-temperature pre-carbonization to obtain biomass pre-carbonized carbon; S3, physical activation: the pre-carbonized carbon is placed in an activation atmosphere to perform medium-temperature activation, and biomass activated carbon is obtained; S4, high-temperature carbonization: the biomass activated carbon is placed in an inert atmosphere to perform high-temperature carbonization, and a hard carbon intermediate is obtained; S5, chemical vapor deposition coating: the hard carbon intermediate is placed in a mixed atmosphere of a coating carbon source and an inert gas to perform chemical vapor deposition coating, and a surface-coated biomass hard carbon negative electrode material is obtained. The application can realize a higher closed pore volume at a milder temperature, and the synergistic regulation pore forming mode of activating and forming pores first and then high-temperature closing pores also avoids the insufficient closed pores caused by single high-temperature treatment.

Description

Technical Field

[0001] This invention relates to the technical field of sodium-ion battery energy storage, and in particular to a hard carbon anode material for sodium-ion batteries based on stepwise synergistic regulation and its preparation method. Background Technology

[0002] Sodium-ion batteries have shown great application potential in large-scale energy storage systems and low-speed electric vehicles due to the abundance, low cost, and wide distribution of sodium resources. As a key component of sodium-ion batteries, the performance of the anode material directly affects the battery's energy density, cycle life, and rate performance. Hard carbon materials, due to their unique disordered carbon structure and the coexistence of graphite-like microcrystals, can achieve efficient sodium-ion storage through the synergy of "slope region" and "plateau region," and are considered one of the most promising sodium-ion battery anode materials for industrialization.

[0003] The sodium storage performance of hard carbon is closely related to its internal pore structure, especially the capacity of the plateau region, which mainly depends on the number, size, and distribution of closed pores. The main methods for constructing closed pores include: 1) extreme high-temperature treatment (>1600℃), which can promote local graphitization and closed pore formation, but has extremely high energy consumption and a limited number of closed pores; 2) chemical activation methods (such as KOH activation), which can effectively create pores and achieve partial closed pore conversion, but uses highly corrosive reagents, posing environmental pollution and safety risks; 3) template-assisted methods, which can construct closed pores through precursor design, but the template removal process is complex and has low production efficiency. These methods generally suffer from problems such as complex processes, high costs, and poor environmental compatibility, which limit their large-scale application.

[0004] Chemical vapor deposition (CVD) technology is used to modify the surface and adjust the pore structure of carbon materials. This technology decomposes carbon source gas at high temperature and deposits pyrolytic carbon layers on the material surface and in the pores, thereby accurately sealing open pores and constructing closed pores in situ. For example, Chinese patent document CN116534835A discloses a vapor deposition preparation method for hard carbon anode materials for sodium-ion batteries, including: (1) pre-carbonization; (2) pulverization; (3) vapor phase coating; (4) high-temperature carbonization. This method places the vapor phase coating step before high-temperature carbonization, which may cause the coating layer structure to be destroyed in the subsequent high-temperature process, resulting in an excessively high specific surface area of ​​the material, which in turn induces the continuous overgrowth of the SEI film during cycling and accelerates capacity decay. In addition, Chinese patent document CN119284882B discloses A method for regulating the microstructure of biomass-based hard carbon using vapor deposition (CVD), along with biomass-based hard carbon anode materials and their applications, has been proposed. However, this method struggles to form sufficient closed-pore structures during carbonization, resulting in a low sodium storage plateau capacity and hindering the improvement of full-cell energy density. Furthermore, simply using CVD to modify pre-formed carbon substrates has significant limitations. The CVD effect heavily relies on the initial pore structure of the substrate; if the substrate has insufficient openings or an undesirable structure, it is difficult to achieve sufficient closed-pore construction. Moreover, the precision of controlling the size and distribution of closed pores during deposition is limited, easily leading to overfilling or incomplete sealing, affecting sodium storage stability. Therefore, developing a preparation method that can synergistically regulate the internal pore structure and surface interface chemistry of hard carbon, while possessing structural precision, process simplicity, and environmental friendliness, has become a key challenge in promoting the practical application of hard carbon anodes. Summary of the Invention

[0005] The purpose of this invention is to solve the problems in the prior art and propose a method for preparing hard carbon anode materials for sodium-ion batteries based on stepwise synergistic regulation. Through a stepwise coupling strategy of pre-carbonization-physical activation-high temperature carbonization-CVD coating, the precise construction of closed-pore structures and the synergistic optimization of surface interface chemistry are achieved, thereby obtaining hard carbon anode materials with high specific capacity, high first-cycle coulombic efficiency, excellent rate performance and long-cycle stability.

[0006] To achieve the above objectives, this invention proposes a method for preparing a hard carbon anode material for sodium-ion batteries based on stepwise synergistic regulation, comprising the following steps: S1. Biomass pretreatment: The biomass is preliminarily cleaned, dried, and crushed to obtain coconut shell precursor; S2. Low-temperature precarbonization: The precursor is precarbonized at low temperature to construct a stable carbon skeleton and obtain biomass precarbonized carbon. S3. Physical activation: The pre-carbonized carbon is placed in an activation atmosphere for medium-temperature activation to obtain biomass activated carbon; S4. High-temperature carbonization: The biomass activated carbon is placed in an inert atmosphere for high-temperature carbonization to obtain a hard carbon intermediate; S5. Chemical vapor deposition coating: The hard carbon intermediate is placed in a mixed atmosphere of coating carbon source and inert gas for chemical vapor deposition coating to obtain a surface-coated biomass hard carbon anode material.

[0007] Preferably, the biomass is coconut shell.

[0008] Coconut shells, as a widely available, dense, and low-ash biomass raw material, offer an ideal precursor for the preparation of high-performance hard carbon due to their natural hierarchical pore structure and low impurity characteristics.

[0009] Preferably, the low-temperature pre-carbonization temperature of step S2 is lower than the physical activation temperature of step S3, and the physical activation temperature of step S3 is lower than the high-temperature carbonization temperature of step S4.

[0010] Preferably, in step S2, the low-temperature pre-carbonization temperature is 200-600℃, the carbonization time is 60-240min, and the heating rate is 2-10℃ / min.

[0011] Preferably, in step S2, the low-temperature pre-carbonization temperature atmosphere is nitrogen or argon, and the gas flow rate is 50-300 ml / min.

[0012] Preferably, in step S3, the activation temperature is 500-800℃, the activation time is 1-6h, and the heating rate is 2-10℃ / min.

[0013] Preferably, in step S3, the activation atmosphere is CO2 or water vapor, and the gas flow rate is 50-300 ml / min.

[0014] Preferably, in step S4, the high-temperature carbonization temperature is 900-1700℃, the carbonization time is 2-6h, and the heating rate is 2-10℃ / min.

[0015] Preferably, in step S4, the high-temperature carbonization atmosphere is nitrogen or argon, and the gas flow rate is 50-300 ml / min.

[0016] Preferably, in step S5, the carbon source gas coated by chemical vapor deposition is one or more of methane, ethane, propane, and n-butane, the volume ratio of the carbon source gas to the inert gas is 5:1 to 1:5, and the total gas flow rate is 50-300 mL / min.

[0017] Preferably, in step S5, the chemical vapor deposition coating temperature is 700-1000℃ and the coating time is 30-120min.

[0018] This invention also proposes a coconut shell hard carbon anode material prepared by the aforementioned method, wherein the closed-pore volume of the coconut shell hard carbon anode material is 0.20-0.30 cm³. 3 / g, specific surface area is 5-10m² 2 / g, interlayer spacing d 002 The wavelength is 0.36-0.38 nm.

[0019] This invention also proposes the application of the coconut shell hard carbon anode material in the preparation of hard carbon anodes for sodium-ion batteries.

[0020] The beneficial effects of this invention are: First, this invention uses a two-step method of physical activation and high-temperature carbonization to create pores. In the activation stage, controllable open pore channels are introduced to provide a structural basis for the subsequent formation of closed pores. In the high-temperature carbonization stage, the ordering of graphite microcrystals is promoted, and thermally induced pore shrinkage and closure are induced at the edges of the formed open pores. Compared with the existing pore-creating method of direct high-temperature carbonization, this invention can achieve a higher closed pore volume at a milder temperature. Moreover, the synergistic control of pore-creating by first activating and then closing the pores at high temperature avoids the insufficient number of closed pores caused by a single high-temperature treatment. Secondly, this invention uses physical activation such as CO2 instead of chemical activation such as KOH, avoiding the corrosiveness, safety risks and cumbersome subsequent washing and impurity removal steps caused by the use of strong alkali; CO2 activation selectively etches carbon atoms through gas-solid reaction to form a uniformly distributed porous structure, providing an ideal substrate surface for subsequent CVD deposition. Third, this invention places CVD coating after high-temperature carbonization, rather than directly coating the initial porous carbon; the hard carbon intermediate formed after high-temperature carbonization has a preliminary closed-pore structure and a more stable carbon skeleton. When CVD deposition is performed at this time, the carbon layer can be deposited more evenly at the pore opening and surface, realizing the directional transformation from open-pore structure to closed-pore structure and avoiding the blind filling of internal pores. Fourth, this invention alters the initial contact interface between the electrode and electrolyte by constructing a uniform and dense carbon coating layer on the hard carbon surface. This coating layer has a low defect density and controllable surface chemistry, which preferentially guides the electrolyte decomposition to form a thin and dense solid electrolyte interface (SEI) mainly composed of inorganic components such as NaF and Na2O. Compared with uncoated or unevenly coated samples, this SEI layer has higher ionic conductivity and better mechanical stability, effectively suppressing continuous side reactions and SEI thickening during cycling. At the same time, the coating layer significantly reduces the specific surface area of ​​the material, reducing sodium loss caused by irreversible electrolyte decomposition, thereby significantly improving the first coulombic efficiency (>92%). Furthermore, the closed pores formed during the coating process provide a stable environment for the storage of "sodium clusters," significantly increasing the plateau capacity (>75%), thus solving the industry problem of balancing high first efficiency and high plateau capacity. Fifth, the entire process involved in this invention is a continuous tubular furnace heat treatment process with clear steps and easily controllable parameters, eliminating the need for complex steps such as template removal and post-treatment with strong acids and alkalis. The entire process does not use highly corrosive or toxic chemicals. The main byproducts of CO2 activation and CVD coating are CO and H2, which can be discharged or recycled through simple treatment, conforming to the concept of green manufacturing. Using waste coconut shells as the main raw material, it achieves high-value utilization of biomass resources, with a wide range of sources and significantly lower costs than preparation methods based on petrochemical precursors or fine chemicals. Furthermore, the equipment involved consists of conventional tubular furnaces, with mild process conditions, easy scale-up, and good industrialization prospects.

[0021] The features and advantages of the present invention will be described in detail through embodiments and in conjunction with the accompanying drawings. Attached Figure Description

[0022] Figure 1 The XRD patterns of Examples 1-3 and Comparative Example 1 of this invention are shown below. Figure 2 These are HRTEM and SEM images of embodiments 1-3 of the present invention; Figure 3 The charge-discharge curve of the battery obtained by using the hard carbon material of Example 1 of the present invention as the negative electrode material of a sodium-ion battery is shown. Figure 4 This is a charge-discharge curve of a battery obtained by using the hard carbon material of Example 2 of the present invention as a negative electrode material for a sodium-ion battery. Figure 5 The charge-discharge curve of the battery obtained by using the hard carbon material of Example 3 of the present invention as the negative electrode material of a sodium-ion battery is shown. Figure 6 The charge-discharge curve of the battery obtained by using the hard carbon material of Example 4 of the present invention as the negative electrode material of a sodium-ion battery is shown. Figure 7 The charge-discharge curve of the battery obtained by using the hard carbon material of Comparative Example 1 of the present invention as the negative electrode material of a sodium-ion battery is shown. Figure 8 The charge-discharge curve of the battery obtained by using the hard carbon material of Comparative Example 2 of the present invention as the negative electrode material of a sodium-ion battery is shown. Figure 9 This is a charge-discharge curve of the battery obtained by using the hard carbon material of Comparative Example 3 of the present invention as the negative electrode material of a sodium-ion battery.

[0023] Figure 1 In the XRD pattern, the horizontal axis is 2θ (°) and the vertical axis is the diffraction intensity (au).

[0024] Figures 3 to 9 In the figure, the horizontal axis of the charge-discharge curve represents the specific capacity (mAh / g), and the vertical axis represents the potential (V) relative to sodium ions. Detailed Implementation

[0025] Example 1 A hard carbon anode material for sodium-ion batteries based on stepwise synergistic regulation is prepared by the following method: S1. The coconut shells are initially cleaned, dried, and crushed to obtain biomass coconut shells; S2. The washed biomass coconut shells are initially crushed and sieved to 8-20 mesh, then transferred to a tube furnace and pre-carbonized at 600°C under a nitrogen atmosphere for 2 hours to obtain pre-carbonized carbon. The heating rate is 5°C / min and the gas flow rate is 200ml / min. S3. After pre-carbonization, switch to CO2 atmosphere, adjust the flow rate to 100 ml / min, and perform a physical activation process from room temperature to 800℃ for 2 hours to obtain coconut shell activated carbon, wherein the heating rate is 5℃ / min. S4. After cooling to room temperature, switch to argon atmosphere and heat from room temperature to 1400℃ for 2 hours of high-temperature carbonization. The heating rate is set to 5℃ / min and 2℃ / min before and after 1000℃, respectively. After naturally cooling to room temperature, collect the biomass coconut shell hard carbon intermediate. S5. After cooling to room temperature, switch to a nitrogen-methane mixed atmosphere, with a methane-argon ratio of 1:1 and a total flow rate of 100 ml / min; heat from room temperature to 900 °C for CVD coating for 30 min at a heating rate of 5 °C / min; cool to room temperature and collect coconut shell coated hard carbon.

[0026] Example 2 In this embodiment, S5 is heated from room temperature to 900°C for 60 minutes for CVD coating, and the rest is the same as in Embodiment 1.

[0027] Example 3 In this embodiment, S5 is heated from room temperature to 900°C for 90 minutes for CVD coating, and the rest is the same as in Embodiment 1.

[0028] Example 4 In this embodiment, the carbon source for coating in the CVD coating step of S5 is replaced with n-butane, and the gas flow rate is switched to 60 ml / min, wherein the ratio of n-butane to nitrogen is 1:5, and other aspects are the same as in Example 1.

[0029] Example 5 In this embodiment, S2 is pre-carbonized for 2 hours by raising the temperature from room temperature to 200°C, and the rest is the same as in Embodiment 1.

[0030] Example 6 In this embodiment, S2 is pre-carbonized for 1 hour by raising the temperature from room temperature to 400°C, and the rest is the same as in Embodiment 1.

[0031] Example 7 In this embodiment, coconut shell activated carbon is obtained by physically activating S3 by raising the temperature from room temperature to 650°C for 4 hours. Other steps are the same as in Example 1.

[0032] Example 8 In this embodiment, S3 is obtained by physically activating coconut shell carbon by heating from room temperature to 500°C for 6 hours. Other steps are the same as in Example 1.

[0033] Example 9 In this embodiment, S3 is obtained by physically activating coconut shell carbon by heating from room temperature to 800°C for 1 hour. Other steps are the same as in Example 1.

[0034] Example 10 In this embodiment, S4 is heated from room temperature to 900°C for 6 hours of high-temperature carbonization, and the rest is the same as in Embodiment 1.

[0035] Example 11 In this embodiment, S4 is heated from room temperature to 1700°C for 4 hours of high-temperature carbonization, and the rest is the same as in Embodiment 1.

[0036] Example 12 In this embodiment, after S5 is cooled to room temperature, it is switched to a nitrogen-methane mixed atmosphere, wherein the ratio of methane to argon is 5:1 and the total flow rate is 50 ml / min; the temperature is then raised from room temperature to 700°C for 30 min of CVD coating.

[0037] Example 13 In this embodiment, after S5 is cooled to room temperature, it is switched to a nitrogen-methane mixed atmosphere, wherein the ratio of methane to argon is 1:5 and the total flow rate is 300 ml / min; the temperature is then raised from room temperature to 1000°C for 120 min of CVD coating.

[0038] Comparative Example 1 The coconut shell-coated hard carbon in this comparative example differs from that in Example 2 in only one aspect in its preparation method: The CVD coating step of S5 is removed, and the coconut shell hard carbon intermediate is collected after high-temperature carbonization of S3 and applied to the negative electrode of sodium-ion battery.

[0039] Comparative Example 2 The coconut shell hard carbon in this comparative example differs from that in Example 2 in only one aspect in its preparation method: The high-temperature carbonization reaction step of S4 is removed, and coconut shell activated carbon is directly coated by CVD and applied to the negative electrode of sodium-ion batteries.

[0040] Comparative Example 3 The coconut shell-coated hard carbon in this comparative example differs from that in Example 2 in the following two aspects in terms of preparation method: 1. Delete the high-temperature carbonization reaction step of S4; 2. The CVD coating step of S5 is removed, and the coconut shell activated carbon is directly collected and applied to the negative electrode of sodium-ion battery.

[0041] Test case I. Structural Analysis The crystal structure of coconut shell hard carbon was analyzed using X-ray electron diffraction. The XRD pattern is shown below. Figure 1 As shown.

[0042] Examples 1-3 and Comparative Example 1 all exhibited typical (002) and (100) characteristic peaks.

[0043] The interlayer spacing d of Examples 1-3 and Comparative Example 1 was calculated based on Bragg's equation. 002 The values ​​were 0.373, 0.369, 0.363, and 0.375 nm, all within the range of 0.36-0.4 nm, suitable for Na... + The insertion and extraction of graphite; with the extension of deposition time, the (002) diffraction peak shifts significantly to the right and the half-width at half-maximum of the diffraction peak gradually narrows, indicating that the interlayer spacing of graphite gradually decreases and the orderliness of the crystal structure is enhanced.

[0044] The microstructure of Examples 1-3 was analyzed using high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM), such as... Figure 2 As shown.

[0045] The present invention relates to a method for preparing hard carbon materials that exhibit a typical highly disordered structure with abundant defects and distorted graphite-like microcrystals inside. As the coating time increases, the continuity and orientation order of the graphite lattice fringes of the sample gradually improve, and significant structural regularization is observed along the crystal plane extension direction and the stacking thickness direction. At the same time, moderate coating promotes the homogenization of the carbon material surface, but excessive deposition of pyrolytic carbon causes the original particles to be wrapped and bonded by the carbon layer to form irregular agglomerates.

[0046] The specific surface areas of Examples 1-3 and Comparative Examples 1-4 were obtained using nitrogen isothermal adsorption-desorption curves, and the results are summarized in Table 1.

[0047] The specific surface area of ​​the hard carbon materials obtained by the preparation method of this invention in Examples 1-3 is all less than 10 m². 2 / g, a smaller specific surface area inhibits the formation of the SEI film, thereby improving the first-cycle coulombic efficiency; the closed-cell volume of Examples 1-3 was obtained using true density testing. The increase in closed-cell volume is significant for improving the plateau capacity. The closed-cell volumes of the hard carbon materials corresponding to Examples 1-3 reached 0.21, 0.26, and 0.24 cm³, respectively. 3 / g.

[0048] II. Electrochemical Performance Testing 1. Button cell battery assembly The biomass coconut shell hard carbon prepared in Examples 1-3 was used as the negative electrode to assemble CR2032 coin cells for electrochemical performance testing.

[0049] The specific steps are as follows: Coconut shell-based hard carbon sample, binder (CMC), and conductive carbon black (Super P) are mixed uniformly in a mass ratio of 8:1:1 using a mixer. Before mixing, an appropriate amount of deionized water is added to adjust the viscosity of the slurry. The slurry is uniformly coated onto copper foil using a 10-micron-high scraper and vacuum dried in a vacuum oven at 80°C for 12 hours to form an electrode. The copper foil is cut into electrode discs with a diameter of 12 mm, and the active material loading of the electrode discs is approximately 1.5~1.8 mg. The half-cell assembly process is completed in a glove box filled with argon atmosphere (water and oxygen concentrations are both less than 0.01 ppm). 1M NaPF6 in diglyme and Whatman GF / D glass fiber are used as the electrolyte and separator, respectively. The prepared electrode discs are used as the negative electrode, and the sodium sheet is used as the positive electrode. They are then packaged with the separator, electrolyte, gasket, spring sheet, and positive and negative electrode shells in the assembly sequence to form a 2032 coin cell half-cell.

[0050] 2. Electrochemical performance testing Constant current charge-discharge tests were performed on a LANHE CT3002 battery testing system (LANHE, Wuhan, China). The voltage window for the test was 0.001-3V, and the test current was 0.1C. 1C is defined as 300mA / g.

[0051] The test results are summarized in Table 1.

[0052]

[0053] The biomass coconut shell hard carbon obtained by the preparation method of this invention exhibits excellent electrochemical performance, including extremely high reversible capacity and first-cycle coulombic efficiency. Example 2, in particular, demonstrates a high specific capacity of 412.1 mAh / g and an ICE of 92.5%, with a plateau capacity of 310 mAh / g, representing over 75% of the total capacity. The charge-discharge curves are shown below. Figure 4 As shown; compared to Example 1 ( Figure 3 Example 2 shows more complete pyrolytic carbon deposition, achieving the closure of more open pores and providing additional space for sodium ion storage; however, the further extension of the coating time did not lead to a sustained increase in platform capacity. Example 3 ( Figure 5The reversible capacity and ICE of the sample declined, mainly because the pyrolytic carbon deposition tended to saturate after 60 min. Over-coating led to shrinkage of the closed pore size and reduced interlayer spacing. The highly graphitized structure inhibited the limited intercalation of sodium ions, resulting in a decrease in sodium storage efficiency. Due to the presence of a large number of open pore structures, the coconut shell activated carbon of Comparative Example 3, which was not treated with high-temperature carbonization and CVD, only showed a typical slope-type voltage curve. Figure 9 The ICE was low (68.1%); the plateau curves of Comparative Example 1, which underwent only high-temperature carbonization, and Comparative Example 2, which underwent only CVD treatment, gradually became apparent, and the capacity improvement was mainly concentrated in the plateau region, such as... Figure 6 and 7 As shown; compared to the methane-coated sample, the sample in Example 4, which uses n-butane as the coating gas source, Figure 8 The reversible capacity and ICE were both lower than those in Example 2. This may be because the n-butane cracking pathway is more complex, making it difficult to construct a uniform, dense, and effective coating layer, which in turn affects ion transport.

[0054] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the present invention are within the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon anode material for sodium-ion batteries based on stepwise synergistic regulation, characterized in that, Includes the following steps: S1. Biomass pretreatment: The biomass is pre-cleaned, dried and crushed to obtain biomass precursors; S2. Low-temperature precarbonization: The precursor is precarbonized at low temperature to construct a stable carbon skeleton and obtain biomass precarbonized carbon. S3. Physical activation: The pre-carbonized carbon is placed in an activation atmosphere for medium-temperature activation to obtain biomass activated carbon; S4. High-temperature carbonization: The biomass activated carbon is placed in an inert atmosphere for high-temperature carbonization to obtain a hard carbon intermediate; S5. Chemical vapor deposition coating: The hard carbon intermediate is placed in a mixed atmosphere of coating carbon source gas and inert gas for chemical vapor deposition coating to obtain a surface-coated biomass hard carbon anode material.

2. The preparation method of sodium-ion battery hard carbon anode material based on stepwise synergistic regulation as described in claim 1, characterized in that: The biomass is coconut shell.

3. The preparation method of sodium-ion battery hard carbon anode material based on stepwise synergistic regulation as described in claim 1, characterized in that: The low-temperature pre-carbonization temperature of step S2 is lower than the physical activation temperature of step S3, and the physical activation temperature of step S3 is lower than the high-temperature carbonization temperature of step S4.

4. The preparation method of sodium-ion battery hard carbon anode material based on stepwise synergistic regulation as described in claim 1, characterized in that: In step S2, the temperature of the low-temperature pre-carbonization is 200-600℃, the carbonization time is 60-240 min, and the heating rate is 2-10℃ / min; the carbonization atmosphere is nitrogen or argon.

5. The preparation method of sodium-ion battery hard carbon anode material based on stepwise synergistic regulation as described in claim 1, characterized in that: In step S3, the physical activation temperature is 500-800℃, the activation time is 1-6h, the heating rate is 2-10℃ / min, and the activation atmosphere is CO2 or water vapor.

6. The preparation method of sodium-ion battery hard carbon anode material based on stepwise synergistic regulation as described in claim 1, characterized in that: In step S4, the high-temperature carbonization temperature is 900-1700℃, the carbonization time is 2-6h, and the heating rate is 2-10℃ / min; the atmosphere for the high-temperature carbonization is nitrogen or argon.

7. The preparation method of sodium-ion battery hard carbon anode material based on stepwise synergistic regulation as described in claim 1, characterized in that: In step S5, the carbon source gas coated by chemical vapor deposition is one or more of methane, ethane, propane, and n-butane, the volume ratio of carbon source gas to inert gas is 5:1 to 1:5, and the total gas flow rate is 50-300 mL / min.

8. The preparation method of sodium-ion battery hard carbon anode material based on stepwise synergistic regulation as described in claim 1, characterized in that: In step S5, the temperature for chemical vapor deposition coating is 700-1000℃, and the coating time is 30-120 min.

9. The coconut shell hard carbon anode material obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The closed-cell volume of the coconut shell hard carbon anode material is 0.20-0.30 cm³. 3 / g, specific surface area is 5-10m² 2 / g, interlayer spacing d 002 The wavelength is 0.36-0.38 nm.

10. The coconut shell hard carbon anode material as described in claim 9, characterized in that: The coconut shell-based hard carbon is used to prepare hard carbon anodes for sodium-ion batteries.

Images