Pore-regulated carbon material and its regulation method and application

Abstract

This invention belongs to the technical field of secondary battery anode materials, and provides a pore-controlled carbon material, its control method, and its application. The method includes the following steps: mixing a carbon precursor, a solvent, and a porous carbon material to obtain a mixed solution; sequentially subjecting the mixed solution to heat treatment and carbonization treatment to complete the pore control of the porous carbon material. This invention can control the pore type, pore volume, specific surface area, open pore size, and interface state of the final carbon material by changing the type of carbon precursor, solution concentration, heat treatment temperature and pressure, and carbonization temperature and heating rate. The resulting material, when used as an anode material for sodium-ion batteries, can achieve a simultaneous and significant improvement in low-potential plateau, initial coulombic efficiency, rate performance, and cycle stability, while also exhibiting excellent capacity retention at low temperatures.

Description

Technical Field

[0001] This invention relates to the field of secondary battery anode material technology, and in particular to a carbon material with pore control, its control method, and its application. Background Technology

[0002] With the continuous development of various portable devices, new energy vehicles, and energy storage systems, there is an urgent need to find low-cost, high-performance clean energy sources. The operating voltage of a battery is determined by the voltage difference between the positive and negative electrodes, which necessitates that the voltage of the negative electrode be as low as possible. Therefore, developing sodium-ion battery anode materials with a low voltage platform, high initial coulombic efficiency, good rate performance, and cycle stability is crucial. This will lay the foundation for the successful construction of high-performance anode materials for rapid sodium storage at low potential in full cells in the future.

[0003] Hard carbon materials, after processing, possess abundant closed-pore structures. When used as anode materials in sodium-ion batteries, sodium ions fill these closed pores, resulting in a significant low-potential plateau. Porous carbon is low-cost and high-yield, making it widely used in supercapacitors. However, when used in sodium-ion batteries, its highly porous structure and highly disordered lattice limit sodium storage to adsorption, resulting in only a slope and a very low initial coulombic efficiency. Therefore, adjusting its pore structure is necessary. Researchers have used techniques such as template carbonization and physical / chemical activation pore size control to regulate the pore size of carbon materials, employing methods like pre-oxidation, material composites, and vapor deposition to control microcrystals. However, these methods are complex to operate and rely on single precursors, and their electrochemical performance has not seen a breakthrough improvement when used as anode materials in sodium-ion batteries.

[0004] Therefore, it is of great significance to find a method to modulate the pore structure of hard carbon anode materials for sodium-ion batteries by preparing them from porous carbon, so as to improve the tap density, first coulombic efficiency and low voltage plateau performance of porous carbon anode materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a pore-controlled carbon material, its control method and application. The pore-controlled carbon material is applied to the anode material of sodium-ion batteries, which has high initial coulombic efficiency, high rate performance, excellent cycle stability and low potential plateau.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for controlling the pore size of porous carbon materials, comprising the following steps:

[0008] A carbon precursor, solvent, and porous carbon material are mixed to obtain a mixed solution; the mixed solution is then subjected to heat treatment and carbonization treatment in sequence to complete the pore control of the porous carbon material.

[0009] Preferably, the carbon precursor includes one or more of coal tar pitch, petroleum pitch, chitosan, and phenolic resin.

[0010] The solvent includes one or more of tetrahydrofuran, xylene, n-hexane, ethanol, and pyridine;

[0011] The specific surface area of ​​the porous carbon material is 20–5000 m². 2 / g.

[0012] Preferably, the mass-to-volume ratio of carbon precursor, solvent, and porous carbon material is 1 g: 10–30 mL: 0.01–10 g.

[0013] Preferably, the pressure of the heat treatment is -0.01 to -10 MPa.

[0014] Preferably, the heat treatment temperature is 30–200°C and the heat treatment time is 0.5–48 h.

[0015] Preferably, the carbonization process is carried out under an inert atmosphere, which is nitrogen or argon.

[0016] Preferably, the carbonization treatment pressure is -5 to 0.1013 MPa.

[0017] Preferably, the heating rate of the carbonization treatment is 0.5 to 20 °C / min, the target temperature of the carbonization treatment is 1100 to 2000 °C, and the holding time after reaching the target temperature is 0.5 to 8 h.

[0018] The present invention also provides a pore-controlled carbon material obtained by the pore control method of the aforementioned porous carbon material.

[0019] The present invention also provides the application of the pore-controlled carbon material in sodium-ion battery anode materials.

[0020] The beneficial effects of this invention are:

[0021] This invention provides a method for controlling the pore size of porous carbon materials, comprising the following steps: mixing a carbon precursor, a solvent, and the porous carbon material to obtain a mixed solution; and sequentially subjecting the mixed solution to heat treatment and carbonization treatment to complete the pore control of the porous carbon material. This invention, by controlling the pore structure of porous carbon materials, designs and forms a hard carbon anode for use in sodium-ion batteries, broadening the application fields of porous carbon materials. Through a specific heat treatment process (reduced pressure drying process), this invention can promote the entry of small-molecule carbon precursors in the solution into the near-surface pore structure of the porous carbon material, adjusting the pore volume, pore size, and specific surface area without causing the formation of a coating layer at the two-phase interface and surface.

[0022] This invention modulates the pore structure in a hierarchical manner from the outside in. On one hand, by appropriately sealing the pore structure near the surface of the porous carbon material through heat treatment (reduced pressure drying process), the pore size and specific surface area are controlled, resulting in a hard carbon anode for sodium-ion batteries. This transforms the sloping sodium storage behavior into a low-potential plateau sodium storage behavior (low-pressure plateau capacity reaches 224 mAh / g), achieving an initial coulombic efficiency improvement to 88%. On the other hand, the internal pore structure of the porous carbon material is preserved, which can promote Na... + The diffusion behavior in the bulk phase of the material at low temperatures enables the resulting hard carbon material to exhibit excellent electrochemical performance at low temperatures, with a plateau capacity retention rate of 100% at -10℃ and 85% at -20℃.

[0023] This invention controls the pore shape, pore volume, specific surface area, open pore size, and surface and interface state of the final carbon material by changing the type of carbon precursor, solution concentration, heat treatment temperature and pressure, as well as carbonization temperature and heating rate. The regulated carbon material is conducive to the closed-pore filling of sodium ions, thereby optimizing battery performance. When used as a negative electrode material for sodium-ion batteries, the resulting material can achieve a simultaneous and significant improvement in low potential plateau, initial coulombic efficiency, rate performance, and cycle stability, while also exhibiting excellent capacity retention at low temperatures. Attached Figure Description

[0024] Figure 1 This is a transmission electron microscope (TEM) image of the carbon material after pore control in Example 1.

[0025] Figure 2 The charge-discharge curves of the sodium-ion battery in Example 1 at room temperature are shown (Specific Capacity, Potential, Voltage).

[0026] Figure 3 The charge-discharge curves of the sodium-ion battery in Example 3 at different temperatures are shown (Specific Capacity, Potential, Voltage).

[0027] Figure 4 The charge-discharge curves of the sodium-ion battery in Comparative Example 1 at room temperature are shown (Specific Capacity, Potential, Voltage).

[0028] Figure 5 The image shows the transmission electron microscopy (TEM) characterization of the carbon material in Comparative Example 3.

[0029] Figure 6 The charge-discharge curves of the sodium-ion battery in Comparative Example 3 at room temperature are shown (Specific Capacity, Potential, Voltage).

[0030] Figure 7 The nitrogen adsorption-desorption curves of the carbon materials after pore control in Examples 1-4 are shown (Relative Pressure, Adsorbed Volume). Detailed Implementation

[0031] This invention provides a method for controlling the pore size of porous carbon materials, comprising the following steps:

[0032] A carbon precursor, solvent, and porous carbon material are mixed to obtain a mixed solution; the mixed solution is then subjected to heat treatment and carbonization treatment in sequence to complete the pore control of the porous carbon material.

[0033] In this invention, the carbon precursor preferably includes one or more of coal tar pitch, petroleum pitch, chitosan, and phenolic resin.

[0034] In this invention, the solvent preferably includes one or more of tetrahydrofuran, xylene, n-hexane, ethanol, and pyridine.

[0035] In this invention, the porous carbon material is preferably activated carbon; the tap density of the porous carbon material is preferably 0.2–1 g / mL, more preferably 0.29–0.85 g / mL, and even more preferably 0.37–0.56 g / mL; the specific surface area of ​​the porous carbon material is preferably 20–5000 m². 2 / g, further preferably 23-2915m 2 / g, more preferably 1642~2187m 2 / g.

[0036] In this invention, the synthesis process of porous carbon materials is simple and the raw materials are abundant, but their pore structure is an open pore obtained by etching, and they are often used as simple adsorbents or catalyst carriers. This invention regulates the pore structure of porous carbon materials and designs to form hard carbon anodes, which are suitable for the field of sodium-ion batteries and improve the high added value of porous carbon materials.

[0037] In this invention, the preferred mass-to-volume ratio of carbon precursor, solvent, and porous carbon material is 1g:10-30mL:0.01-10g, more preferably 1g:12-28mL:0.5-8g, and even more preferably 1g:15-25mL:1-3g.

[0038] In this invention, the mixing preferably includes the following steps: first, fully dissolving the carbon precursor in a solvent to obtain a carbon precursor solution, and then dispersing the porous carbon material in the carbon precursor solution to obtain a mixed solution.

[0039] In this invention, the heat treatment pressure is preferably -0.01 to -10 MPa, more preferably -1 to -8 MPa, and even more preferably -2 to -5 MPa.

[0040] In this invention, the heat treatment temperature is preferably 30-200°C, more preferably 60-150°C, and even more preferably 80-100°C; the heat treatment time is preferably 0.5-48h, more preferably 5-40h, and even more preferably 8-20h.

[0041] In this invention, after the heat treatment is completed, the solid powder is collected and carbonized.

[0042] In this invention, the carbonization process is preferably carried out under an inert atmosphere, preferably nitrogen or argon.

[0043] In this invention, the pressure of the carbonization treatment is preferably -5 to 0.1013 MPa, more preferably -3 to 0.1 MPa, and even more preferably -2 to -0.1 MPa.

[0044] In this invention, the heating rate of the carbonization treatment is preferably 0.5–20 °C / min, more preferably 3–18 °C / min, and even more preferably 5–15 °C / min; the target temperature of the carbonization treatment is preferably 1100–2000 °C, more preferably 1300–1900 °C, and even more preferably 1400–1700 °C; and the holding time after reaching the target temperature is preferably 0.5–8 h, more preferably 2–6 h, and even more preferably 3–5 h.

[0045] In this invention, the carbonization treatment is preferably a segmented heating carbonization treatment. Specifically, the carbonization treatment includes a first carbonization treatment and a second carbonization treatment performed sequentially. The temperature of the first carbonization treatment is preferably 1100-1300℃, more preferably 1150-1250℃, and even more preferably 1200℃. The heating rate from room temperature to the temperature of the first carbonization treatment is preferably 5-20℃ / min, more preferably 8-18℃ / min, and even more preferably 10-15℃ / min. The temperature of the second carbonization treatment is preferably 1400-2000℃, more preferably 1500-1900℃, and even more preferably 1600-1700℃. The heating rate from the temperature of the first carbonization treatment to the temperature of the second carbonization treatment is preferably 0.5-3℃ / min, more preferably 1-2.5℃ / min, and even more preferably 1.5-2℃ / min. The holding time after reaching the temperature of the second carbonization treatment is preferably 0.5-8h, more preferably 2-6h, and even more preferably 3-5h.

[0046] In this invention, a specific heat treatment process (reduced pressure drying process) can promote the entry of small molecule carbon precursors in solution into the near-surface pore structure of porous carbon materials, adjusting pore volume, pore size, and specific surface area without causing the formation of a coating layer at the two-phase interface and surface; while traditional chemical vapor deposition, surface coating, and composite methods lead to the formation of heterogeneous coating layers on the material surface, hindering the formation of Na+. + The electrolyte diffuses into the material, resulting in significant polarization at the two-phase interface.

[0047] The present invention also provides a pore-controlled carbon material obtained by the pore control method of the aforementioned porous carbon material.

[0048] The present invention also provides the application of the pore-controlled carbon material in sodium-ion battery anode materials.

[0049] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0050] Example 1

[0051] Weigh 0.3g of activated carbon (tapered density 0.56g / mL, specific surface area 23m²) at a mass ratio of 3:1. 2 / g), 0.1g coal tar pitch; first, fully dissolve the coal tar pitch in 2mL tetrahydrofuran to obtain a coal tar pitch solution, then add activated carbon and stir to disperse it evenly to obtain a mixed solution. The mixed solution is then subjected to heat treatment. The heat treatment conditions are: drying in a vacuum drying oven at -0.1MPa and 60℃ for 8h. After the heat treatment, collect the solid powder, put it in a magnetic boat, and place it in a tube furnace for carbonization under a nitrogen atmosphere. The carbonization pressure is set to 0.1013MPa, and the temperature is increased to 1200℃ at a heating rate of 5℃ / min, and then increased to 1500℃ at a heating rate of 2℃ / min. The temperature is held at 1500℃ for 2h to obtain the pore-controlled carbon material.

[0052] The pore-controlled carbon material prepared in this embodiment was characterized by transmission electron microscopy (TEM), resulting in the TEM image of the pore-controlled carbon material in this embodiment, as shown below. Figure 1 As shown. From Figure 1 As can be seen, the carbon material after pore control contains a large number of short-range graphite microcrystal regions and closed-pore structures generated by microcrystal stacking.

[0053] In this embodiment, the pore-controlled carbon material has a blocky surface with a specific surface area of ​​25 m². 2 / g, tap density is 0.67g / mL, I D / I G The value is 1.42.

[0054] A sodium-ion battery was prepared using the pore-controlled carbon material obtained in this embodiment. The steps are as follows: The pore-controlled carbon material, sodium carboxymethyl cellulose, and carbon black were weighed at a mass ratio of 8:1:1, homogenized, coated onto copper foil, dried, and cut to obtain battery electrodes. The obtained battery electrodes were then used as the working electrode, and the sodium electrode as the counter electrode. The sodium-ion battery was assembled in a glove box. Electrochemical performance tests were performed (using a CT2001A blue electric test system at room temperature of 25°C). The charge-discharge curves of the sodium-ion battery in this embodiment at room temperature were obtained, as shown below. Figure 2 As shown; Figure 2 In the diagram, 1st represents the first charge-discharge cycle, 2nd represents the second charge-discharge cycle, and 3rd represents the third charge-discharge cycle. From... Figure 2 As can be seen, the material exhibits an initial coulombic efficiency of 70.8% and a low discharge / charge voltage plateau (a low-potential plateau capacity of 224 mAh / g at a current density of 20 mA / g). Electrochemical performance tests at low temperatures revealed a reversible capacity of 218 mAh / g at -10°C, with a low-potential plateau capacity of 122 mAh / g.

[0055] Example 2

[0056] Weigh 0.2g of activated carbon (tapered density 0.37g / mL, specific surface area 1642m²) at a mass ratio of 1:1. 2 / g), 0.2g coal tar pitch, first fully dissolve the coal tar pitch in 4mL tetrahydrofuran to obtain a coal tar pitch solution, then add activated carbon and stir to disperse it evenly to obtain a mixed solution. The mixed solution is then heat-treated under the following conditions: drying in a vacuum drying oven at -0.1MPa and 60℃ for 8h. After the heat treatment, the solid powder is collected, placed in a magnetic boat, and placed in a tube furnace for carbonization under a nitrogen atmosphere. The carbonization pressure is set to 0.1013MPa, and the temperature is increased to 1200℃ at a heating rate of 5℃ / min, then increased to 1500℃ at a heating rate of 2℃ / min, and held at 1500℃ for 2h to obtain the pore-controlled carbon material.

[0057] In this embodiment, the pore-controlled carbon material has a blocky surface with a specific surface area of ​​54 m². 2 / g, tap density is 0.69g / mL, the material contains a large number of short-range graphite microcrystal regions and closed-pore structures formed by microcrystal stacking, I D / I G The value is 1.58.

[0058] Sodium-ion batteries were prepared using the pore-controlled carbon material obtained in this embodiment, following the same steps as in Example 1. Electrochemical performance tests revealed that the material exhibits a high initial coulombic efficiency of 81%, a low discharge / charge voltage plateau (a low-potential plateau capacity of 144 mAh / g at a current density of 20 mA / g), a reversible capacity retention of 91% after 50 cycles at a current density of 20 mA / g, demonstrating excellent cycle stability and high-rate performance, and a reversible capacity of 186 mAh / g at -10°C, including a low-potential plateau capacity of 108 mAh / g.

[0059] Example 3

[0060] Weigh 0.1g of activated carbon (tapered density 0.29g / mL, specific surface area 2187m²) at a mass ratio of 0.5:1. 2 / g), 0.2g coal tar pitch, first fully dissolve the coal tar pitch in 2mL tetrahydrofuran to obtain a coal tar pitch solution, then add activated carbon and stir to disperse it evenly to obtain a mixed solution. The mixed solution is then heat-treated under the following conditions: drying in a vacuum drying oven at -0.1MPa and 60℃ for 8h. After the heat treatment, the solid powder is collected, placed in a magnetic boat, and placed in a tube furnace for carbonization under a nitrogen atmosphere. The carbonization pressure is set to 0.1013MPa, and the temperature is increased to 1200℃ at a heating rate of 5℃ / min, then increased to 1500℃ at a heating rate of 2℃ / min, and held at 1500℃ for 2h to obtain the pore-controlled carbon material.

[0061] In this embodiment, the pore-controlled carbon material has a blocky surface with a specific surface area of ​​40 m². 2 / g, tap density is 0.70g / mL, the material contains a large number of short-range graphite microcrystal regions and closed-pore structures formed by microcrystal stacking, I D / I G The value is 1.57.

[0062] A sodium-ion battery was prepared using the pore-controlled carbon material obtained in this embodiment, following the same steps as in Example 1. Electrochemical performance tests were performed, and charge-discharge curves of the sodium-ion battery at different temperatures were obtained, as shown below. Figure 3 As shown. From Figure 3As can be seen, the material exhibits a high initial coulombic efficiency of 86%, a low discharge / charge voltage plateau (low-potential plateau capacity of 178 mAh / g at a current density of 20 mA / g), and a reversible capacity retention of 88% after 50 cycles at a current density of 20 mA / g, demonstrating excellent cycle stability and high rate performance. At -10℃, the reversible capacity is 255 mAh / g, with a low-potential plateau capacity of 185 mAh / g, indicating complete retention of the low-potential plateau capacity (100%). At -20℃, the reversible capacity is 216 mAh / g, with a low-potential plateau capacity of 152 mAh / g, indicating a plateau capacity retention of 85%.

[0063] Example 4

[0064] Weigh 0.1g of activated carbon (tapered density 0.20g / mL, specific surface area 2915m²) at a mass ratio of 0.5:1. 2 / g), 0.2g coal tar pitch, first fully dissolve the coal tar pitch in 2mL tetrahydrofuran to obtain a coal tar pitch solution, then add activated carbon and stir to disperse it evenly to obtain a mixed solution. The mixed solution is then heat-treated under the following conditions: drying in a vacuum drying oven at -0.1MPa and 60℃ for 8h. After the heat treatment, the solid powder is collected, placed in a magnetic boat, and placed in a tube furnace for carbonization under a nitrogen atmosphere. The carbonization pressure is set to 0.1013MPa, and the temperature is increased to 1200℃ at a heating rate of 5℃ / min, then increased to 1500℃ at a heating rate of 2℃ / min, and held at 1500℃ for 2h to obtain the pore-controlled carbon material.

[0065] In this embodiment, the pore-controlled carbon material has a blocky surface with a specific surface area of ​​46 m². 2 / g, tap density is 0.69g / mL, the material contains a large number of short-range graphite microcrystal regions and closed-pore structures formed by microcrystal stacking, I D / I G The value is 1.58.

[0066] Sodium-ion batteries were prepared using the pore-controlled carbon material obtained in this embodiment, following the same steps as in Example 1. Electrochemical performance tests revealed a low discharge / charge voltage plateau (170 mAh / g low-potential plateau capacity at 20 mA / g current density); after 50 cycles at 20 mA / g current density, the reversible capacity retention was 84%, demonstrating excellent cycle stability and high-rate performance; the reversible capacity at -10°C was 254 mAh / g, with a low-potential plateau capacity of 170 mAh / g, indicating complete retention of the low-potential plateau capacity; and the reversible capacity at -20°C was 220 mAh / g, with a low-potential plateau capacity of 160 mAh / g, showing high retention of both total capacity and plateau capacity.

[0067] Example 5

[0068] Weigh 0.1g of activated carbon (tapered density 0.29g / mL, specific surface area 2187m²) at a mass ratio of 0.5:1. 2 / g), 0.2g coal tar pitch, first fully dissolve the coal tar pitch in 2.5mL xylene to obtain a coal tar pitch solution, then add activated carbon and stir to disperse it evenly to obtain a mixed solution. The mixed solution is then heat-treated under the following conditions: drying in a vacuum drying oven at -0.1MPa and 60℃ for 8h. After the heat treatment, the solid powder is collected, placed in a magnetic boat, and placed in a tube furnace for carbonization under a nitrogen atmosphere. The carbonization pressure is set to 0.1013MPa, and the temperature is increased to 1200℃ at a heating rate of 5℃ / min, then increased to 1500℃ at a heating rate of 2℃ / min, and held at 1500℃ for 2h to obtain the pore-controlled carbon material.

[0069] In this embodiment, the pore-controlled carbon material has a blocky surface with a specific surface area of ​​41 m². 2 / g, tap density is 0.70g / mL, the material contains a large number of short-range graphite microcrystal regions and closed-pore structures formed by microcrystal stacking, I D / I G The value is 1.58.

[0070] Sodium-ion batteries were prepared using the pore-controlled carbon material obtained in this embodiment, following the same steps as in Example 1. Electrochemical performance testing revealed that the material exhibits a high initial coulombic efficiency of 88%, a low discharge / charge voltage plateau, and a reversible capacity retention of 89% after 50 cycles at a current density of 20 mA / g, demonstrating excellent cycle stability and high rate performance.

[0071] Example 6

[0072] Weigh 0.1g of activated carbon (tapered density 0.29g / mL, specific surface area 2187m²) at a mass ratio of 0.5:1. 2 / g), 0.2g coal tar pitch, first fully dissolve the coal tar pitch in 4mL n-hexane to obtain a coal tar pitch solution, then add activated carbon and stir to disperse it evenly to obtain a mixed solution. The mixed solution is then heat-treated under the following conditions: drying in a vacuum drying oven at -0.1MPa and 60℃ for 8h. After the heat treatment, the solid powder is collected, placed in a magnetic boat, and placed in a tube furnace for carbonization under a nitrogen atmosphere. The carbonization pressure is set to 0.1013MPa, and the temperature is increased to 1200℃ at a heating rate of 5℃ / min, then increased to 1500℃ at a heating rate of 2℃ / min, and held at 1500℃ for 2h to obtain the pore-controlled carbon material.

[0073] In this embodiment, the pore-controlled carbon material has a blocky surface with a specific surface area of ​​43 m². 2 / g, tap density is 0.71g / mL, the material contains a large number of short-range graphite microcrystal regions and closed-pore structures formed by microcrystal stacking, I D / I G The value is 1.57.

[0074] Sodium-ion batteries were prepared using the pore-controlled carbon material obtained in this embodiment, following the same steps as in Example 1. Electrochemical performance testing revealed that the material exhibits a high initial coulombic efficiency of 84%, a low discharge / charge voltage plateau, and a reversible capacity retention of 86% after 50 cycles at a current density of 20 mA / g, demonstrating excellent cycle stability and high rate performance.

[0075] Comparative Example 1

[0076] With other conditions remaining unchanged in Example 3, the heat treatment was carried out in a forced-air drying oven at a pressure of 0.1013 MPa to obtain carbon material.

[0077] The carbon material prepared in this comparative example has a blocky surface and a specific surface area of ​​46 m². 2 / g, tap density is 0.67g / mL, the material contains long-range graphite-like regions and a large number of porous structures, I D / I G The value is 1.20.

[0078] A sodium-ion battery was prepared using the carbon material described in this example, following the same steps as in Example 1. Its electrochemical performance was then tested, yielding the charge-discharge curves of the sodium-ion battery in this comparative example at room temperature, as shown below. Figure 4 As shown; Figure 4 In the diagram, 1st represents the first charge-discharge cycle, 2nd represents the second charge-discharge cycle, and 3rd represents the third charge-discharge cycle. From... Figure 4 As can be seen, the material has an initial coulombic efficiency of 65% and a low potential plateau capacity of 110 mAh / g at a current density of 20 mA / g.

[0079] Comparative Example 2

[0080] Weigh 0.1g of activated carbon (tapered density 0.29g / mL, specific surface area 2187m²) at a mass ratio of 0.5:1. 20.2 g of coal tar pitch was added to a zirconia ball mill jar. At the same time, four zirconia grinding balls with a diameter of 6 mm and eight zirconia grinding balls with a diameter of 12 mm were added to the ball mill jar. The mixture was ball milled at a speed of 200 r / min for 4 hours. After the ball milling was completed, the material was placed in a magnetic boat and placed in a tube furnace for carbonization under a nitrogen atmosphere. The carbonization pressure was set to 0.1013 MPa. The temperature was increased to 1200℃ at a heating rate of 5℃ / min, and then increased to 1500℃ at a heating rate of 2℃ / min. The mixture was held at 1500℃ for 2 hours to obtain the carbon material.

[0081] The carbon material prepared in this comparative example has a blocky surface and a specific surface area of ​​85 m². 2 / g.

[0082] Sodium-ion batteries were prepared using the carbon material prepared in this proportion, following the same steps as in Example 1. Electrochemical performance tests revealed that the material's low-potential plateau was only 115 mAh / g, and its specific capacity at a current density of 20 mA / g was 249 mAh / g.

[0083] Comparative Example 3

[0084] Activated carbon (with a tap density of 0.29 g / mL and a specific surface area of ​​2187 m²) was used. 2 / g) is placed in a magnetic boat and placed in a tube furnace for carbonization under a nitrogen atmosphere. The carbonization pressure is set to 0.1013 MPa, and the temperature is increased to 1200℃ at a heating rate of 5℃ / min, and then increased to 1500℃ at a heating rate of 2℃ / min. The temperature is held at 1500℃ for 2 hours to obtain the carbon material.

[0085] Transmission electron microscopy (TEM) characterization images of carbon materials in this comparative example are shown below. Figure 5 As shown. From Figure 5 As can be seen, the carbon material has a blocky surface with a specific surface area of ​​1766 m². 2 / g, with a highly disordered microcrystalline structure and well-developed pore structure.

[0086] A sodium-ion battery was prepared using the carbon material described in this example, following the same steps as in Example 1. Its electrochemical performance was then tested, yielding the charge-discharge curves of the sodium-ion battery in this comparative example at room temperature, as shown below. Figure 6 As shown; from Figure 6 As can be seen, the material's initial coulombic efficiency is 20%, there is no low potential plateau, and the specific capacity is only 100 mAh / g at a current density of 20 mA / g.

[0087] As can be seen from Examples 1-6 and Comparative Example 1, only reduced pressure heat treatment can yield carbon materials with pore structure control. If a forced-air drying oven is used for drying heat treatment, only a simple mixture of porous carbon and pitch can be obtained, which cannot achieve the effect of pore structure control.

[0088] According to Examples 1-6, it should be noted that the amount of carbon precursor used for pore control varies for porous carbon materials with different pore structures. The larger the specific surface area of ​​the porous carbon material and the more developed the pore structure, the more carbon precursor is required. If the amount of carbon precursor is too small, the pore structure cannot be completely filled; if the amount of carbon precursor is too large, a large amount of filler material will remain on the material surface, completely masking the performance of the pore-controlled carbon material.

[0089] As can be seen from Examples 1-6 and Comparative Examples 1-3, the pore-controlled carbon material described in this invention exhibits higher initial coulombic efficiency, better cycle stability, and higher low-voltage capacity compared to conventional carbon materials. When the pore-controlled carbon materials obtained in Examples 1-6 are used as anode materials for sodium-ion batteries, the materials possess high initial coulombic efficiency and a low discharge / charge voltage plateau. The porous carbon material with a larger pore structure, after pore control, exhibits high reversible capacity, high and low potential plateaus, excellent cycle stability, and high rate performance at low temperatures.

[0090] Finally, the pore-controlled carbon materials prepared in Examples 1-4 were subjected to nitrogen adsorption-desorption performance tests, and the nitrogen adsorption-desorption curves of the pore-controlled carbon materials in Examples 1-4 were obtained, as shown in the figure. Figure 7 As shown. From Figure 7 It can be seen that in the low-pressure region, the pore-controlled carbon materials prepared in Examples 2, 3, and 4 rise rapidly, indicating that they contain a large number of micropores. In the medium-pressure region, the pore-controlled carbon material prepared in Example 4 exhibits more mesopores and a larger specific surface area.

[0091] As can be seen from the above embodiments, by changing the type of carbon precursor, solution concentration, heat treatment temperature and pressure, and carbonization temperature and heating rate, the present invention can control the pore shape, pore volume, specific surface area, open pore size and surface and interface state of the final carbon material. The regulated carbon material is conducive to the closed pore filling of sodium ions, thereby optimizing battery performance. When the obtained material is used as a negative electrode material for sodium-ion batteries, it can achieve a simultaneous and significant improvement in low potential plateau, first coulombic efficiency, rate performance and cycle stability, while also having excellent capacity retention in low temperature environments.

[0092] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the pore size of porous carbon materials, characterized in that, Includes the following steps: First, the carbon precursor is fully dissolved in a solvent to obtain a carbon precursor solution. Then, the porous carbon material is dispersed in the carbon precursor solution to obtain a mixed solution. The mixed solution is then subjected to heat treatment and carbonization treatment in sequence to complete the pore control of the porous carbon material. The carbon precursor includes one or more of coal tar pitch, petroleum pitch, chitosan, and phenolic resin. The heat treatment pressure is -0.01 to -10 MPa; The heat treatment temperature is 30–200°C, and the heat treatment time is 0.5–48 h.

2. The pore control method for porous carbon materials as described in claim 1, characterized in that, The solvent includes one or more of tetrahydrofuran, xylene, n-hexane, ethanol, and pyridine; The specific surface area of ​​the porous carbon material is 20–5000 m². 2 / g.

3. The pore control method for porous carbon materials as described in claim 1 or 2, characterized in that, The mass-volume ratio of carbon precursor, solvent and porous carbon material is 1g:10-30mL:0.01-10g.

4. The pore control method for porous carbon materials as described in claim 1, characterized in that, The carbonization process is carried out under an inert atmosphere, which is either nitrogen or argon.

5. The pore control method for porous carbon materials as described in claim 1 or 4, characterized in that, The carbonization process is carried out at a pressure of -5 to 0.1013 MPa.

6. The pore control method for porous carbon materials as described in claim 5, characterized in that, The heating rate of the carbonization process is 0.5–20 °C / min, the target temperature of the carbonization process is 1100–2000 °C, and the holding time after reaching the target temperature is 0.5–8 h.

7. The pore-controlled carbon material obtained by the pore control method of any one of claims 1 to 6.

8. The application of the pore-controlled carbon material as described in claim 7 in sodium-ion battery anode materials.

Images