A method for preparing pitch-based hard carbon material based on anti-solvent interface limited deposition

Abstract

The application discloses a pitch-based hard carbon material and a preparation method and application thereof, and belongs to the technical field of sodium ion batteries. Pitch is dissolved in an organic solvent to form an organic phase dispersion liquid, natural polysaccharide is dispersed in water to form an aqueous phase dispersion liquid, and under shearing conditions, the pitch is in-situ deposited, embedded and coated at the polysaccharide chain segment, colloidal particles and water / organic phase interface through anti-solvent interface confinement deposition, so as to form a liquid phase interpenetrating composite precursor. After drying and stage heating carbonization, the pitch-based hard carbon material with a closed pore structure is obtained. During the carbonization process, the polysaccharide is pyrolyzed to form a sacrificial microcavity, and the pitch pyrolysis product is deposited at the pore opening for secondary condensation, so as to realize self-sealing of the pore opening. When the obtained material is used as a negative electrode of a sodium ion battery, the low potential platform capacity and initial coulombic efficiency can be improved.

Description

[0001] and its applications Technical Field This invention belongs to the field of secondary battery technology, specifically relating to a method for preparing pitch-based hard carbon material and its application in the negative electrode of sodium-ion batteries. Background Technology

[0002] Sodium-ion batteries are considered an important electrochemical energy storage system for large-scale energy storage due to the abundance of sodium resources, low cost, and relatively high safety. The anode material is one of the key factors determining the energy density, rate performance, and cycle life of sodium-ion batteries. Among them, hard carbon materials, with their large interlayer spacing, abundant disordered microcrystalline structure, and low sodium storage potential, are considered one of the most promising anode materials for sodium-ion batteries for industrialization.

[0003] Asphalt is an important carbon source for preparing hard carbon materials due to its wide availability, low cost, high carbonization yield, and tunable molecular structure. However, asphalt is prone to liquid-phase carbonization during high-temperature carbonization, where its aromatic molecules migrate, condense, and stack in an ordered manner in a softened and molten state, forming a graphitized microcrystalline structure. The (002) interplanar spacing of this type of structure is typically only 0.34-0.36 nm, which is smaller than the critical interlayer spacing (approximately 0.37 nm) required for effective sodium ion insertion, resulting in low sodium storage capacity and low potential plateau capacity. Therefore, how to suppress the ordered rearrangement during asphalt carbonization and regulate the evolution of pore structure is a key issue in the research of asphalt-based hard carbon materials.

[0004] Existing technologies mainly employ pre-oxidative crosslinking and composite modification methods to regulate asphalt-based hard carbon. The pre-oxidative crosslinking method introduces oxygen-containing functional groups into the asphalt molecules, restricting the migration and stacking of aromatic lamellae; however, the degree of crosslinking is difficult to control uniformly, limiting its ability to constrain carbonization behavior. Composite modification involves combining asphalt with hard carbon precursors such as biomass, resins, or sugars, utilizing the disordered carbon structure to inhibit the ordered stacking of asphalt. Based on the different composite methods, existing technologies are mainly divided into the following two categories: The first type is solid-phase ball milling, which physically mixes asphalt and hard carbon precursors through mechanical ball milling. This method can only achieve physical contact at the micrometer scale, resulting in weak interfacial bonding and easy phase separation during carbonization. Asphalt can still migrate freely and stack orderly during the melting stage, offering limited constraint. The second type is homogeneous solution blending, which dissolves asphalt and hard carbon precursors together in an organic solvent and removes the solvent by drying to achieve molecular-level mixing. While this method improves mixing uniformity, the two components are prone to re-aggregation during drying, making it difficult to form stable nanoscale interpenetrating structures. More importantly, the gases generated by polysaccharide pyrolysis during carbonization easily escape and cannot be effectively captured by the asphalt to form closed pores, leading to uncontrollable closed-pore structures and making it difficult to simultaneously achieve low-potential plateau capacity and initial coulombic efficiency.

[0005] In summary, existing technologies for combining asphalt with hard carbon precursors are mainly limited to "solid-solid mixing" or "homogeneous solution mixing," lacking an interface control method that can induce selective deposition of asphalt on the surface of hard carbon precursors in the liquid phase, rather than self-aggregation or uniform precipitation.

[0006] To address the aforementioned issues, this invention proposes an antisolvent interface confined deposition strategy: utilizing the characteristic that asphalt is "soluble in organic solvents but insoluble in water," an organic phase dispersion containing asphalt aromatic components is introduced into a natural polysaccharide aqueous phase dispersion system. Under the action of solvent exchange and antisolvent, the asphalt transforms from a dissolved state to an interface deposition state, and precipitates in situ at polysaccharide microregions such as polysaccharide segments, colloidal particles, and the water / organic phase interface, resulting in embedding and coating, forming a liquid-penetrating composite precursor in which the asphalt phase and natural polysaccharide microregions are interleaved at the nanoscale. The core advantages of this strategy are: (1) The deposition process of asphalt is dominated by the interface confinement effect rather than random aggregation, thus achieving precise control of the composite structure; (2) The polysaccharide micro-regions serve as “capture sites” to ensure that asphalt and polysaccharides are tightly combined at the nanoscale, forming a stable interpenetrating network structure; (3) In the subsequent carbonization process, the polysaccharide micro-regions pyrolyze to form sacrificial microcavities, which become dispersed confinement units that restrict the continuous flow and long-range migration of the asphalt phase in the softening stage, thus transforming the asphalt from free liquid phase carbonization to confined softening coating; at the same time, the aromatic intermediates generated by asphalt cracking migrate, accumulate and re-condense at the pore openings and inner walls, realizing the self-sealing of the pore openings and the in-situ construction of the closed-pore structure, thereby simultaneously achieving the suppression of asphalt ordering, the expansion of interlayer spacing and the control of the closed-pore structure.

[0007] The present invention aims to provide a pitch-based hard carbon material based on antisolvent interface confined deposition, its preparation method, and its application. The preparation method is simple and low-cost, utilizing the antisolvent effect to drive in-situ deposition of pitch on the surface of natural polysaccharide microregions, forming a nanoscale liquid-interpenetrating composite precursor. After carbonization, a pitch-based hard carbon material with a high closed-pore ratio, expanded interlayer spacing, and a quasi-graphite microcrystalline structure is obtained. When used as a negative electrode in sodium-ion batteries, the resulting material exhibits high reversible specific capacity, low potential plateau capacity, and initial coulombic efficiency.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for preparing pitch-based hard carbon materials based on antisolvent interface confined deposition includes the following steps: (1) Dissolve asphalt in an organic solvent to obtain an organic phase dispersion, and disperse natural polysaccharides in water to obtain an aqueous phase dispersion; (2) The organic phase dispersion is added to the aqueous phase dispersion. The antisolvent effect of asphalt being soluble in organic solvents but insoluble in water is used to precipitate and deposit asphalt on the polysaccharide surface. After drying, a liquid-penetrating composite precursor is obtained. (3) The composite precursor is subjected to staged heating carbonization treatment under an inert atmosphere to obtain asphalt-based hard carbon material.

[0009] Preferably, the organic solvent in step (1) is selected from one or more of N-methylpyrrolidone, tetrahydrofuran, quinoline, pyridine, toluene, xylene, and ethanol / tetrahydrofuran mixed solvent; the mass concentration of the asphalt in the organic phase dispersion is 10-25 wt%.

[0010] Preferably, the natural polysaccharide in step (1) is selected from one or more of alginic acid, corn starch, and apple pectin; the amount of natural polysaccharide added is 50-100% of the mass of asphalt.

[0011] Preferably, the organic phase dispersion in step (2) is introduced into the aqueous phase dispersion system by dropping, with a dropping rate of 1-10 mL / min, and interface deposition is carried out under stirring or shearing conditions.

[0012] Preferably, the solvent removal method in step (2) includes vacuum drying after filtration, with a drying temperature of 60-120 °C and a drying time of 6-24 h.

[0013] Preferably, the staged heating carbonization process in step (3) includes segmented heat treatment and high-temperature carbonization; the segmented heat treatment is: holding at 180-280 °C for 1-6 h, holding at 300-480 °C for 0.5-4 h, and holding at 500-850 °C for 0.5-3 h; the high-temperature carbonization temperature is 1200-1500 °C, the holding time is 1-3 h, and the heating rate is 2-10 °C / min.

[0014] Preferably, the inert atmosphere in step (3) is at least one of nitrogen, argon or helium.

[0015] The present invention also provides a pitch-based hard carbon material prepared by the above preparation method. Preferably, the hard carbon material has a closed-cell structure and a quasi-graphite microcrystalline structure, and its (002) interplanar spacing is 0.36-0.40 nm.

[0016] The present invention also provides a sodium-ion battery negative electrode, wherein the negative electrode comprises the above-mentioned pitch-based hard carbon material.

[0017] This invention also provides the application of the aforementioned pitch-based hard carbon material as a negative electrode material for sodium-ion batteries. This invention constructs a pitch / natural polysaccharide interpenetrating composite precursor via an antisolvent interfacial confined deposition method, transforming the pitch from a dissolved state in the organic phase to an interfacial deposition state in an aqueous environment, preferentially depositing it on the surface of the natural polysaccharide and around its dispersed micro-regions. Compared to solid-phase ball milling, this method can improve the interfacial contact between pitch and natural polysaccharides, allowing the natural polysaccharides to simultaneously serve as interfacial trapping sites, a dispersed confining phase, and a source of sacrificial microcavities in the precursor.

[0018] In the subsequent stage of heated carbonization, the natural polysaccharide microregions first undergo dehydration, pyrolysis, and partial carbonization, releasing oxygen-containing volatiles and forming sacrificial microcavities within the asphalt phase. During the softening stage, the asphalt phase locally coats these microcavities, restricting the thermoplastic flow of the asphalt by the polysaccharide dispersed phase and the interfacial deposition structure. As the temperature continues to rise, tar-like aromatic intermediates and oligomeric fused-ring aromatic fragments generated from asphalt pyrolysis migrate, accumulate, and undergo secondary condensation deposition at the pore openings and inner walls of the microcavities, gradually shrinking the gas release channels and achieving pore self-sealing. Through the aforementioned interfacial deposition, restricted softening coating, and pore self-sealing processes, the long-range migration and excessive stacking of aromatic lamellars during asphalt carbonization are suppressed, and the carbon layers undergo short-range rearrangement under restricted conditions, forming an asphalt-based hard carbon material with a closed-pore structure, increased interlamellar spacing, and a quasi-graphite microcrystalline structure.

[0019] In this process, the number of high-energy defects and disordered openings on the carbon material surface is effectively controlled, thereby reducing electrolyte decomposition and SEI film formation during the first charge-discharge cycle. Thus, without the need for thick coating, strong activation, or extremely high carbonization temperatures, a synergistic improvement in the initial coulombic efficiency and reversible specific capacity of pitch-based hard carbon materials can be achieved: the reversible specific capacity is 321.1 mAh g⁻¹. -1 The platform contribution was 194.0 mAh g. -1 The initial Coulomb efficiency is 90.4%. Attached Figure Description

[0020] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the pitch-based hard carbon material prepared in Example 1 of this invention. Figure 2 This is a high-resolution transmission electron microscope (HRTEM) image of the pitch-based hard carbon material prepared in Example 1 of the present invention; Figure 3 The image shows the X-ray diffraction (XRD) pattern of the pitch-based hard carbon material prepared in the comparative example of this invention. Figure 4 The charge-discharge curves of the sodium-ion battery prepared in Example 1 of this invention are shown for the first, second, and third cycles. Figure 5The charge-discharge curves of the sodium-ion battery prepared in Example 2 of this invention are shown for the first, second, and third cycles. Figure 6 The charge-discharge curves of the sodium-ion battery prepared in Example 3 of this invention are shown for the first, second, and third cycles. Figure 7 The above are charge-discharge curves of the sodium-ion battery prepared in the comparative example of this invention for the first, second, and third cycles. Detailed Implementation

[0021] The following specific embodiments further illustrate the method for preparing pitch-based hard carbon materials based on antisolvent interface confined deposition according to the present invention. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0022] The method for preparing pitch-based hard carbon materials provided by this invention includes the following steps: (1) Dissolve asphalt in an organic solvent to obtain an organic phase dispersion, and disperse natural polysaccharides in water to obtain an aqueous phase dispersion; (2) The organic phase dispersion is added to the aqueous phase dispersion. Under shear conditions, the antisolvent effect of asphalt being soluble in organic solvents but insoluble in water is used to cause asphalt to precipitate, deposit and embed on the surface of polysaccharide micro-regions. After drying, a liquid-penetrating composite precursor is obtained. (3) The composite precursor is subjected to staged heating carbonization treatment under an inert atmosphere to obtain asphalt-based hard carbon material.

[0023] In this invention, the natural polysaccharide is selected from one or more of alginic acid, corn starch, or apple pectin.

[0024] During interfacial confined deposition, bituminous molecules undergo interfacial selective precipitation driven by the antisolvent effect, rather than free aggregation, thereby achieving deposition, embedding, and nanoscale interpenetrating structure construction on the surface of polysaccharide microdomains. This structure can be further induced to form a stable closed-pore system during subsequent carbonization.

[0025] During carbonization, polysaccharide microregions first undergo pyrolysis and form sacrificial microcavities, which are then coated by the asphalt phase during the softening stage. Simultaneously, aromatic intermediates generated from asphalt cracking migrate and undergo secondary condensation deposition at the pore openings, achieving self-sealing of the pore openings and in-situ construction of closed-pore structures, thereby effectively inhibiting the formation of open pores.

[0026] The preferred high-temperature carbonization temperature is 1200-1400 ℃, the holding time is 1-3 h, the heating rate is 2-10 ℃ / min, and the atmosphere is argon, nitrogen, or a mixture thereof.

[0027] The method of this invention can significantly regulate the carbonization path of asphalt, suppress excessive ordering of aromatic lamellae, and improve the ability to synergistically regulate interlayer spacing and defect structure.

[0028] Example 1 (1) Dissolve 2 g of asphalt in 20 mL of toluene organic solvent to obtain a 10 wt% asphalt / toluene organic phase dispersion; (2) Disperse 2 g of alginic acid in 200 mL of deionized water, heat to 80 °C, shear and stir at 2000 r / min for 30 min, and then sonicate at 500 W for 30 min to obtain an aqueous dispersion of alginic acid. (3) Under the stirring conditions of 25 ℃ and 500 r / min, the asphalt / toluene organic phase dispersion obtained in step (1) is added dropwise to the alginate aqueous phase dispersion obtained in step (2) at a rate of 5 mL / min. After the addition is completed, stirring is continued for 2 h to allow the asphalt to precipitate and deposit on the surface of the alginate, thus obtaining the liquid-penetrating composite precursor precipitate. (4) The precipitate obtained in step (3) is separated by filtration and dried under vacuum at 80 °C for 12 h; (5) The dried composite precursor was placed in a tube furnace and subjected to staged heating carbonization under an argon atmosphere: the temperature was increased to 270 ℃ at 3 ℃ / min and held for 1 h, then increased to 400 ℃ at 3 ℃ / min and held for 1 h, then increased to 600 ℃ at 3 ℃ / min and held for 1 h, and finally increased to 1300 ℃ at 5 ℃ / min and held for 2 h. The mixture was then naturally cooled to room temperature to obtain asphalt-based hard carbon material.

[0029] The pitch-based hard carbon material in Example 1 was tested using an X-ray diffractometer, and the XRD pattern was obtained. Figure 1 The XRD pattern shows that the angle corresponding to the (002) peak is 23.21°, and the interplanar spacing calculated according to Bragg's formula is 0.3829 nm. Figure 2 The HRTEM image shows a clear closed-pore structure.

[0030] Example 2 By replacing the alginic acid in Example 1 with corn starch, and keeping the other technical features the same as in Example 1, asphalt-based hard carbon material was obtained.

[0031] Example 3 By replacing the alginic acid in Example 1 with apple pectin, and keeping the other technical features the same as in Example 1, asphalt-based hard carbon material was obtained.

[0032] Comparative Example (1) 2 g of asphalt was placed in an argon atmosphere and heated to 1300 °C at a heating rate of 5 °C / min and held for 2 h to obtain asphalt-based hard carbon material without interface confinement control.

[0033] The pitch-based hard carbon material in the comparative example was tested using X-ray diffraction, and its XRD pattern was obtained. Figure 3 The XRD pattern shows that the angle corresponding to the (002) peak is 25.58°, and the interplanar spacing calculated according to Bragg's formula is 0.3480 nm.

[0034] Test Example 1 The asphalt-based hard carbon materials prepared in the comparative examples and Examples 1-3 were mixed with sodium carboxymethyl cellulose at a mass ratio of 95:5 to form a slurry. The slurry was uniformly coated onto a copper current collector foil and dried in an oven at 60 °C for 2 h. The slurry was then cut into circular electrodes with a diameter of 8 mm. After drying the electrodes in a vacuum oven at 120 °C for 10 h, the mass of the active material of the electrodes was weighed and transferred to a glove box. Using sodium metal as the counter electrode and a 1 M solution of NaClO4 dissolved in ethylene carbonate and diethyl carbonate as the electrolyte, CR2025 coin cells were assembled.

[0035] The assembled CR2025 button cells were subjected to charge-discharge performance tests under the following conditions: current density set to 0.1 C (1 C = 300 mA g). -1 The discharge voltage is 0.001 V, and the charging voltage is 3 V.

[0036] Figure 4 The charge-discharge curves of the pitch-based hard carbon material prepared in Example 1 are shown in cycles 1, 2, and 3. Figure 4 It can be seen that the reversible specific capacity for sodium storage in the first cycle of the material described in Example 1 is 321.1 mAh g. -1 The initial coulombic efficiency was 90.4%, and the platform capacity was 194.0 mAh g. -1 ; Figure 5 The charge-discharge curves of the pitch-based hard carbon material prepared in Example 2 are shown in cycles 1, 2, and 3. Figure 5 It can be seen that the reversible specific capacity of sodium storage in the first cycle of the material described in Example 2 is 299.0 mAh g. -1 The initial coulombic efficiency was 88.9%, and the platform capacity was 180.7 mAh g. -1 ; Figure 6 The charge-discharge curves of the pitch-based hard carbon material prepared in Example 3 are shown in cycles 1, 2, and 3. Figure 6 It can be seen that the reversible specific capacity of sodium storage in the first cycle of the material described in Example 3 is 278.9 mAh g. -1 The initial coulombic efficiency was 85.1%, and the platform capacity was 174.5 mAh g. -1 ; Figure 7The charge-discharge curves of the pitch-based hard carbon material prepared for comparison were obtained in cycles 1, 2, and 3; Figure 7 It can be seen that the reversible specific capacity of sodium storage in the first cycle of the material described in the comparative example is 89.20 mAh g. -1 The initial coulombic efficiency was 64.3%, and no plateau sodium storage behavior was observed.

[0037] The relevant parameters and electrochemical test performance of the asphalt-based hard carbon anode materials of Examples 1-3 and the comparative examples are summarized in Table 1 below.

[0038] Other embodiments can be obtained under the premise of innovation, and these embodiments are all within the protection scope of this invention.

[0039] Table 1. Electrochemical test performance of pitch-based hard carbon materials in Implementation (Comparative) Examples 1-3 The experimental results above show that the pitch-based hard carbon material prepared by the present invention has excellent sodium storage capacity and initial coulombic efficiency.

[0040] 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 preparing pitch-based hard carbon materials based on antisolvent interface confined deposition, characterized in that, Includes the following steps: (1) Dissolve asphalt in an organic solvent to obtain an organic phase dispersion, and disperse natural polysaccharides in water to obtain an aqueous phase dispersion; (2) The organic phase dispersion is added to the aqueous phase dispersion. The antisolvent effect of asphalt being soluble in organic solvents but insoluble in water is used to precipitate and deposit asphalt on the polysaccharide surface. After drying, a liquid-penetrating composite precursor is obtained. (3) The composite precursor is subjected to staged heating carbonization treatment under an inert atmosphere to obtain asphalt-based hard carbon material.

2. The preparation method according to claim 1, characterized in that, The organic solvent in step (1) is selected from one or more of N-methylpyrrolidone, tetrahydrofuran, quinoline, pyridine, toluene, xylene, and ethanol / tetrahydrofuran mixed solvent; the mass concentration of the asphalt in the organic phase dispersion is 1-30 wt.

3. The preparation method according to claim 1, characterized in that, The natural polysaccharide mentioned in step (1) is selected from one or more of alginic acid, corn starch, and apple pectin, and the amount of natural polysaccharide added is 25-100% of the mass of asphalt.

4. The preparation method according to claim 1, characterized in that, The organic phase dispersion described in step (2) is introduced into the aqueous phase dispersion system by dropping, with a dropping rate of 1-10 mL / min, and interface deposition is carried out under stirring or shearing conditions.

5. The preparation method according to claim 1, characterized in that, The solvent removal method described in step (2) includes vacuum drying after filtration, with a drying temperature of 60-120 ℃ and a drying time of 6-24 h.

6. The preparation method according to claim 1, characterized in that, The segmented heat treatment described in step (3) includes: Keep warm at 180-280℃ for 1-6 hours; Keep warm at 300-480℃ for 0.5-4 hours; Keep warm at 500-850℃ for 0.5-3 hours; After the segmented heat treatment, the temperature is increased to the high-temperature carbonization temperature of 1200-1500 ℃ at a heating rate of 2-10 ℃ / min, and held for 1-3 h.

7. The preparation method according to claim 1, characterized in that, In the staged heating carbonization process described in step (3), the natural polysaccharide micro-regions undergo pyrolysis before the asphalt to form sacrificial microcavities. The aromatic intermediates produced by the pyrolysis of the asphalt undergo secondary condensation deposition at the pore opening of the microcavities, thereby achieving self-sealing of the pore openings.

8. The pitch-based hard carbon material obtained by the preparation method according to any one of claims 1-7, characterized in that, The hard carbon material has a closed-pore structure with a (002) interplanar spacing of 0.36-0.40 nm.

9. A sodium-ion battery negative electrode, characterized in that, Includes the bitumen-based hard carbon material as described in claim 8.

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