A preparation method of an organic metal salt assisted construction of a multi-closed pore hard carbon material

Abstract

The application belongs to the field of sodium ion battery negative electrode materials, and particularly relates to a preparation method of an organic metal salt assisted construction of a multi-closed pore hard carbon material. The application discloses a preparation method of an organic metal salt assisted construction of a multi-closed pore hard carbon material. The method comprises the following steps: placing pitch powder and starch in a garnet mortar, grinding and sieving to obtain a mixed powder; placing the mixed powder in a tube furnace, heating to 300-500 DEG C, keeping constant temperature for 1-3 hours, and then taking out after cooling to room temperature; placing the obtained material and the organic metal salt in the garnet mortar, grinding and sieving to obtain a precursor material; placing the precursor material in a corundum boat, and transferring to the tube furnace; heating to 1000-1700 DEG C under an inert atmosphere, keeping constant temperature for 1-3 hours, and then obtaining a finished product after natural cooling. The method is simple in process and low in cost, and does not need an additional template removal step. The obtained hard carbon material shows excellent sodium storage performance and cycle stability when used as a sodium ion battery negative electrode.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery anode materials, and particularly relates to a method for preparing a multi-closed-pore hard carbon material assisted by organometallic salts. Background Technology

[0002] While lithium-ion batteries have achieved large-scale application, lithium resources are limited and unevenly distributed, with significant price fluctuations, posing resource security and cost pressures in power batteries and large-scale energy storage scenarios. Therefore, developing energy storage systems based on elements with higher abundance in the Earth's crust is an important technological path to achieve energy structure transformation. Sodium resources are more than 1000 times more abundant than lithium in the Earth's crust and are widely distributed in seawater and mineral salts, making raw material costs low. Sodium-ion batteries (SIBs) are similar in working principle to lithium-ion batteries and have a mature battery manufacturing process, thus being considered a strong competitor in the field of large-scale energy storage. However, the larger radius and higher standard electrode potential of sodium ions place higher demands on electrode structure stability and interface control during intercalation / deintercalation. Especially in terms of anode materials, traditional graphite is difficult to form stable sodium-graphite intercalation compounds, resulting in limited capacity and poor cycle performance. Therefore, developing novel anode materials suitable for sodium-ion storage is one of the core scientific issues in the development of sodium-ion batteries. Research on sodium-ion battery anode materials has begun, for example: Wang Z, Liu W, Tang Y, et al. Regulating closed pores structure of hard carbon anodes to boost plate storage for advanced sodium-ion batteries [J]. Journal of Energy Storage, 2025, 129: 117-379. Xiao S, Guo YJ, Chen HX, et al. Insight into the role of closed-pore size on rate capability of hard carbon for fast-charging sodium-ion batteries [J]. Advanced Materials, 2025, 37(28): 250-1434. Due to the large radius of sodium ions, the insertion and extraction of sodium ions during charging and discharging will cause the carbon material to expand in volume, which can easily cause structural damage and thus affect the cycle stability of the electrode material. In addition, the low sodium storage capacity and energy density are also important factors that limit its further development.

[0003] To address these issues, several improvement methods have been proposed: First, by doping hard carbon with heteroatoms such as nitrogen (N), phosphorus (P), and sulfur (S), the microscopic electronic structure can be modulated to increase defect and active sites and expand interlayer spacing, thereby improving the material's electronic conductivity and sodium storage performance. Second, by constructing composite systems such as hard carbon / metal oxides and hard carbon / carbon-based materials, the synergistic effect between components can be leveraged to optimize charge transport paths and structural stability, thereby improving rate performance and cycle life. Third, by using template methods and heat treatment to introduce closed-pore structures into hard carbon, additional storage space for sodium ions can be provided, and volume changes during charge and discharge processes can be mitigated, thereby improving the material's reversible capacity and cycle stability.

[0004] Selecting suitable additives to construct closed-pore structures is a key research issue. Recent studies have shown that adding organometallic salts as additives can effectively improve the electrochemical performance of hard carbon materials. Furthermore, previous reports have revealed cumbersome experimental methods in the precursor preparation stage, requiring additional steps to remove the additives after the high-temperature carbonization process. This results in high material preparation costs, lengthy experimental times, and stringent preparation conditions, making mass production difficult. Therefore, selecting suitable organometallic salts as additives is crucial. Extensive testing has shown that cadmium acetate as an additive can effectively improve the cycling stability and sodium storage capacity of hard carbon materials at high rate performance. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a method for preparing multi-closed-pore hard carbon materials with the assistance of organometallic salts, which solves the problems of high sodium ion diffusion barrier, low capacity and poor cycle stability of existing sodium-ion battery anode materials, and uses a one-step carbonization method to prepare the material, thus saving costs.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing organometallic salt-assisted closed-pore hard carbon materials includes the following steps: 1) Weigh out asphalt powder and place it in an agate mortar, and add starch at a mass fraction of 30% to 300% relative to the asphalt powder. Grind and sieve to obtain a mixed powder. 2) Place the mixed powder in a tube furnace, heat to 300-500℃, maintain the temperature for 1-3 hours, and then cool to room temperature before removing. 3) Weigh the material obtained in step 2) and place it in an agate mortar. Take an organometallic salt with a mass fraction of 50% to 200% relative to the material obtained in step 2), grind and sieve it to obtain the precursor material. 4) Place the precursor material obtained in step 3) in a corundum boat and transfer it to a tube furnace; heat it to 1000-1700℃ at a heating rate of 2-4℃ / min under an inert atmosphere, hold it for 1-3 hours, and then cool it naturally to obtain the multi-closed-pore hard carbon material.

[0007] The asphalt mentioned in step 1) is at least one of coal tar pitch, ethylene tar pitch, and petroleum pitch.

[0008] The starch mentioned in step 1) is soluble starch.

[0009] The starch mentioned in step 1) is one or more of potato starch, corn starch, cassava starch and sweet potato starch.

[0010] In step 1), the asphalt powder and starch are ground for 1 to 3 hours and then passed through an 80 to 200 mesh sieve.

[0011] In step 3), the material obtained in step 2) is ground with organometallic salt for 1 to 3 hours and then passed through an 80 to 200 mesh sieve.

[0012] The atmosphere inside the tubular furnace described in step 2) is air or oxygen.

[0013] The organometallic salt is at least one of zinc acetate, cadmium acetate, zinc gluconate, cadmium gluconate, zinc citrate, and cadmium citrate.

[0014] The working principle of using cadmium acetate is as follows: During the carbonization process, cadmium acetate is initially reduced to nanoparticles of cadmium oxide, which are uniformly dispersed within the carbon matrix. As the carbonization temperature further increases, the cadmium oxide is further reduced to elemental cadmium and carbon dioxide. Due to the low boiling point of elemental cadmium, it volatilizes directly during carbonization, and the carbon dioxide etching effect leaves more open-pore structures within the carbon matrix. When the carbonization temperature rises above 1000℃, the open pores in the carbon material gradually transform into closed-pore structures as the carbon layer shrinks, leaving more closed-pore structures within the material. Furthermore, at lower carbonization temperatures, organic acid anions react with functional groups in the carbon matrix, generating new functional groups or enhancing the structural stability of the carbon matrix. The synergistic effect of these two factors effectively improves the electrochemical performance of hard carbon materials.

[0015] The inert atmosphere used in the tube furnace described in step 4) is argon or nitrogen.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention uses organometallic salts as additives and asphalt and starch as carbon sources to prepare hard carbon materials with multiple closed-pore structures. When the prepared multi-closed-pore hard carbon materials were applied as anode materials in sodium-ion half-cells, the sodium storage capacity was 248.4–377.5 mAh / g at a current density of 0.1 A / g, and after 100 cycles, the capacity remained at 225.8–341.1 mAh / g, with a capacity retention rate of 72.5%–90.6%. This indicates that the method for preparing hard carbon materials using cadmium acetate as an additive has considerable application prospects. Attached Figure Description

[0017] Figure 1 This is a flowchart of the preparation process for constructing multi-closed-pore hard carbon materials with the assistance of organometallic salts.

[0018] Figure 2 These are XRD patterns of the organometallic salt-assisted construction of multi-closed-pore hard carbon materials prepared in Examples 1, 2, 3, 4 and the comparative examples.

[0019] Figure 3 These are Raman diagrams of the organometallic salt-assisted construction of multi-closed-pore hard carbon materials prepared in Examples 1, 2, 3, 4 and the comparative examples.

[0020] Figure 4 These are XPS images of the organometallic salt-assisted construction of multi-closed-pore hard carbon materials prepared in Examples 1, 2, 3, 4 and the comparative examples.

[0021] Figure 5 These are nitrogen adsorption-desorption curves and pore size distribution diagrams of the organometallic salt-assisted construction of multi-closed-pore hard carbon materials prepared in Examples 1, 2, 3, 4 and the comparative examples.

[0022] Figure 6 The diagram shows the cycling performance of the organometallic salt-assisted construction of multi-closed-pore hard carbon materials prepared in Examples 1, 2, 3, 4 and the comparative examples.

[0023] Figure 7 These are rate performance graphs of the organometallic salt-assisted construction of multi-closed-pore hard carbon materials prepared in Examples 1, 2, 3, 4 and the comparative examples.

[0024] Figure 8 These are small-angle scattering diagrams of the organometallic salt-assisted construction of multi-closed-pore hard carbon materials prepared in Example 3 and Comparative Example 3. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0026] Example See Figure 1 A method for preparing organometallic salt-assisted closed-pore hard carbon materials includes the following steps: 1) Weigh out asphalt powder and place it in an agate mortar, and add starch at a mass fraction of 30% to 300% relative to the asphalt powder. Grind for 1 to 3 hours and then pass it through an 80 to 200 mesh sieve to obtain a mixed powder. The asphalt is at least one of coal tar pitch, ethylene tar pitch, and petroleum asphalt. The starch is soluble starch, and is one or more of potato starch, corn starch, cassava starch, and sweet potato starch.

[0027] 2) Place the mixed powder in a tube furnace with an air or oxygen atmosphere, heat to 300-500°C, maintain the temperature for 1-3 hours, and then cool to room temperature before removing. 3) Weigh the material obtained in step 2) and place it in an agate mortar. Take an organometallic salt with a mass fraction of 50% to 200% relative to the material obtained in step 2), grind it for 1 to 3 hours, and then pass it through an 80 to 200 mesh sieve to obtain the precursor material. The organometallic salt is at least one of zinc acetate, cadmium acetate, zinc gluconate, cadmium gluconate, zinc citrate, and cadmium citrate. 4) Place the precursor material obtained in step 3) in a corundum boat and transfer it to a tube furnace; heat it to 1000-1700℃ at a heating rate of 2-4℃ / min under an inert atmosphere (argon or nitrogen), hold it at that temperature for 1-3 hours, and then cool it naturally to obtain the multi-closed-pore hard carbon material.

[0028] The preparation parameters for the organometallic salt-assisted construction of multi-closed-pore hard carbon materials in the embodiments are shown in Tables 1-3.

[0029] Table 1: Key preparation parameters for each embodiment Table 1 continued: Table 2: Key preparation parameters for each embodiment Table 2 continued: Table 3: Key preparation parameters for each embodiment The preparation method of hard carbon materials includes the following steps: 1) Weigh out ethylene tar pitch powder and place it in an agate mortar, and add soluble starch at a mass fraction of 300% relative to the ethylene tar pitch powder. Grind for 2 hours and then pass through a 150-mesh sieve to obtain a mixed material.

[0030] 2) Place the material obtained in step 1) in a tube furnace, keep it at 400°C for 2 hours in an air atmosphere, and then cool it to room temperature before taking it out.

[0031] 3) Place the mixed powder obtained in step 2) into a corundum boat and transfer it into a tube furnace. Heat the furnace to 1500℃ at a heating rate of 3℃ / min under an argon atmosphere, hold for 2 hours, and then allow it to cool naturally to obtain the hard carbon material.

[0032] The preparation parameters for the comparative organometallic salt-assisted construction of multi-closed-pore hard carbon materials are shown in Table 4.

[0033] Table 4: Key preparation parameters for each comparative example The prepared sample was fabricated into an electrode sheet, and assembled into a button cell in the following order: negative electrode shell, sodium sheet, separator, negative electrode sheet, gasket, spring sheet, and positive electrode shell. The electrochemical performance was then tested.

[0034] Figure 2 The X-ray diffraction (XRD) patterns of the samples prepared in Examples 1, 2, 3, 4, and the comparative examples are shown. The prominent diffraction peak near 24° corresponds to the (002) characteristic peak of the carbon material, and the prominent diffraction peak near 43° corresponds to the (100) characteristic peak of the carbon material. The carbonization temperatures of Comparative Examples 1 to 4 gradually increased. The figures show that as the carbonization temperature increased, the (002) characteristic peak gradually shifted to the right, and the peak intensity gradually increased. This indicates that with increasing carbonization temperature, the degree of graphitization of the material increased, and the interlayer spacing gradually decreased. Comparison with the comparative examples reveals that when the carbonization temperature was the same at 1500°C, the addition of an organometallic salt (cadmium acetate) reduced the degree of graphitization and increased the interlayer spacing. This indicates that the introduction of cadmium acetate effectively inhibited the graphitization process of the carbon matrix and effectively increased the interlayer spacing of the material.

[0035] Figure 3 The Raman spectra of the samples prepared in Examples 1, 2, 3, 4, and the comparative examples are shown below. D / I G It can more intuitively represent the degree of graphitization of materials, I D / I G The higher the value, the lower the graphitization degree and the higher the disorder degree of the material. Calculations show that as the carbonization temperature increases, the I value of the material... D / I G The value gradually decreases, indicating a decrease in disorder, which corresponds to an increase in graphitization. Furthermore, by comparing the I values ​​of the materials before and after the addition of cadmium acetate... D / I G It can be observed that after adding cadmium acetate, its I D / I GThe increase in the value corresponds to a decrease in its graphitization degree, which is consistent with the results of the XRD analysis above.

[0036] Figure 4 The XPS spectra of the samples prepared in Examples 1, 2, 3, 4, and the comparative examples show that all samples are composed of both C and O elements. The material with cadmium acetate introduced exhibits a higher O 1s peak intensity, indicating a higher oxygen content. This is because, after the introduction of cadmium acetate, during the low-temperature carbonization stage, the acetate ions react with the hydroxyl groups inside the carbon matrix, leaving more oxygen-containing functional groups in the carbon matrix, thereby increasing the oxygen content in the material.

[0037] Figure 5 (ab) shows the adsorption-desorption curves and pore size distribution diagrams of the samples prepared in Examples 1, 2, 3, 4, and the comparative example. The figures show that as the carbonization temperature increases, the specific surface area and pore volume of the material gradually decrease. When the temperature reaches 1500℃, almost no open pores are visible in the material, indicating that almost all open pores in the material are transformed into closed pores, thus confirming the formation of a closed-pore structure.

[0038] Figure 6 The graph shows the cycling performance of the samples prepared in Examples 1, 2, 3, 4, and the comparative example at a current density of 0.1 A / g. After 100 cycles, their sodium storage capacities were 225.8 mAh / g, 297.4 mAh / g, 341.1 mAh / g, 298.4 mAh / g, and 286.8 mAh / g, respectively. It can be seen that the sodium storage capacity gradually increases with increasing carbonization temperature, reaching a peak at 1500℃. This is because the closed-pore structure in the material is fully formed at this temperature, resulting in the highest sodium storage capacity under a low-voltage plateau. However, as the carbonization temperature continues to rise, the interlayer spacing of the carbon layers continues to decrease, leading to a decrease in capacity. Furthermore, comparing the cycling performance of the material with added cadmium acetate also shows that the sodium storage capacity is significantly improved after adding cadmium acetate, which is attributed to the increased plateau capacity brought about by the formation of closed pores. In addition, the introduction of more oxygen-containing functional groups into the material during low-temperature carbonization also provides more surface adsorption sites, further increasing the sodium storage capacity. In addition, cadmium acetate effectively inhibits the graphitization process of the material, effectively increases the interlayer spacing of the material, provides a wider transport path for sodium ions, and further enhances the cycling stability of the material.

[0039] Figure 7The graphs show the rate performance of the samples prepared in Examples 1, 2, 3, 4, and the comparative examples at current densities of 0.03 A / g, 0.06 A / g, 0.12 A / g, 0.3 A / g, 0.6 A / g, 1.2 A / g, 2 A / g, 5 A / g, and 10 A / g. The graphs show that the sodium storage capacity of the comparative material without zinc acetate is 312.9 mAh / g, 304.4 mAh / g, 294.6 mAh / g, 275.6 mAh / g, 173.5 mAh / g, 92.9 mAh / g, 54.7 mAh / g, 21.2 mAh / g, and 8.6 mAh / g, respectively. This indicates a considerable sodium storage capacity at low current densities. However, as the current density increases, the sodium storage capacity almost reaches zero, indicating poor structural stability and an inability to support rapid charge and discharge processes, thus exhibiting poor rate performance. When cadmium acetate was introduced into the material, the rate performance increased with increasing carbonization temperature, reaching its optimal level at 1500℃. The sodium storage capacities at different current densities were 384.8 mAh / g, 371.5 mAh / g, 365.5 mAh / g, 350.7 mAh / g, 323.1 mAh / g, 281.2 mAh / g, 228.8 mAh / g, 113.8 mAh / g, and 65.2 mAh / g, respectively. This is mainly attributed to the significant capacity improvement brought about by the introduction of closed pores, and the introduction of more oxygen-containing functional groups at low temperatures, providing more adsorption sites and thus significantly enhancing the rate performance.

[0040] Figure 8 The small-angle scattering (SAXS) plots for Example 3 and Comparative Example 3 show that the small-angle scattering curves of the two samples are similar in the range of q = 0.1–1 Å. -1 The presence of distinct shoulder peaks in all intervals indicates the existence of closed nanopores within the samples. The shoulder peak intensity is higher in Comparative Example 3, suggesting an increase in the size of the closed pores. This indicates that the introduction of cadmium acetate effectively increases the size of the closed pores in the material.

[0041] The lignite-tea oil shell-based hard carbon materials prepared in each embodiment were used as anode materials in sodium-ion half-cells. The capacity and capacity retention after 100 cycles at a current density of 0.1 A / g are shown in Table 5.

[0042] Table 5 The above electrochemical experimental results show that using cadmium acetate as an organometallic salt and introducing it into pitch starch hard carbon materials effectively constructs more closed-cell structures, significantly improves interlayer spacing, and introduces more oxygen-containing functional groups onto the carbon material surface, providing more sodium storage sites. Organometallic salts can play a multi-effect role; the best-performing material exhibits a sodium storage capacity of 384.1 mAh / g at a current density of 0.03 A / g, 377.5 mAh / g at a current density of 0.1 A / g, and 341.1 mAh / g after 100 cycles. -1 With a capacity retention rate of 90.5%, it presents a new direction for the large-scale production of low-cost, high-performance sodium-ion battery anode materials.

Claims

1. A method for preparing a multi-closed-pore hard carbon material assisted by organometallic salts, characterized in that, Includes the following steps: 1) Weigh out asphalt powder and place it in an agate mortar, and add starch at a mass fraction of 30% to 300% relative to the asphalt powder. Grind and sieve to obtain a mixed powder. 2) Place the mixed powder in a tube furnace, heat to 300-500℃, maintain the temperature for 1-3 hours, and then cool to room temperature before removing. 3) Weigh the material obtained in step 2) and place it in an agate mortar. Take an organometallic salt with a mass fraction of 50% to 200% relative to the material obtained in step 2), grind and sieve it to obtain the precursor material. 4) Place the precursor material obtained in step 3) in a corundum boat and transfer it to a tube furnace; heat it to 1000-1700℃ at a heating rate of 2-4℃ / min under an inert atmosphere, hold it for 1-3 hours, and then cool it naturally to obtain the multi-closed-pore hard carbon material.

2. The method for preparing a multi-closed-pore hard carbon material assisted by an organometallic salt according to claim 1, characterized in that, The asphalt mentioned in step 1) is at least one of coal tar pitch, ethylene tar pitch, and petroleum pitch.

3. The method for preparing a multi-closed-pore hard carbon material assisted by an organometallic salt according to claim 1, characterized in that, The starch mentioned in step 1) is soluble starch.

4. The method for preparing a multi-closed-pore hard carbon material assisted by an organometallic salt according to claim 1, characterized in that, The starch mentioned in step 1) is one or more of potato starch, corn starch, cassava starch and sweet potato starch.

5. The method for preparing a multi-closed-pore hard carbon material assisted by an organometallic salt according to claim 1, characterized in that, In step 1), the asphalt powder and starch are ground for 1 to 3 hours and then passed through an 80 to 200 mesh sieve.

6. The method for preparing a multi-closed-pore hard carbon material assisted by an organometallic salt according to claim 1, characterized in that, In step 3), the material obtained in step 2) is ground with organometallic salt for 1 to 3 hours and then passed through an 80 to 200 mesh sieve.

7. The method for preparing a multi-closed-pore hard carbon material assisted by an organometallic salt according to claim 1, characterized in that, The atmosphere inside the tubular furnace described in step 2) is air or oxygen.

8. The method for preparing a multi-closed-pore hard carbon material assisted by an organometallic salt according to claim 1, characterized in that, The organometallic salt is at least one of zinc acetate, cadmium acetate, zinc gluconate, cadmium gluconate, zinc citrate, and cadmium citrate.

9. The method for preparing a multi-closed-pore hard carbon material assisted by an organometallic salt according to claim 1, characterized in that, The inert atmosphere used in the tube furnace described in step 4) is argon or nitrogen.

Images