Pitch-based hard carbon material based on dipolar cycloaddition reaction, method for preparing same, and use thereof

Abstract

The application relates to a pitch-based hard carbon material based on a dipolar cycloaddition reaction, a preparation method and application thereof; a THFS component is separated from original pitch through solvent extraction, then is mixed with aldehyde compounds and N-alkyl glycine compounds to react under heating to obtain a modified pitch precursor, and finally is subjected to carbonization treatment to obtain the pitch-based hard carbon material. The application constructs a covalent crosslinking network through a dipolar cycloaddition reaction before carbonization, fully utilizes components with moderate molecular weight in pitch, avoids excessive graphitization of asphaltene macromolecules and overflow of low-molecular-weight substances in the carbonization process, eliminates negative interference of two types of extreme components on the carbonization process, realizes crosslinking of moderate-molecular-weight substances, significantly improves the platform sodium storage capacity of the material, reduces small molecule escape and defect formation in the carbonization process through the pre-crosslinking network, reduces irreversible capacity loss, and the first coulombic efficiency can reach more than 85%, and the process controllability is strong.

Description

Technical Field

[0001] This invention relates to the field of new energy materials and energy storage technology, specifically to a pitch-based hard carbon material based on a dipole cycloaddition reaction, its preparation method, and its application. Background Technology

[0002] Asphalt, due to its high carbon content, wide availability, and low price, is an ideal precursor for preparing hard carbon anode materials. However, the diversity of asphalt types and the complexity of asphalt molecular structures make the controllable preparation of different asphalt-based hard carbons difficult and the carbonization behavior unclear. Furthermore, because the asphalt structure is mainly composed of polycyclic aromatic hydrocarbons and contains numerous hydrogen atoms and strong π-π interactions between aromatic molecules, direct carbonization of asphalt at high temperatures easily produces highly graphitized soft carbon, characterized by small interlayer spacing and a lack of closed pores.

[0003] Based on the polarity and solubility of the asphalt structure, its components can be divided into: asphaltenes, resins, aromatics, and oils. High molecular weight substances possess the highest aromaticity and readily form highly graphitized microstructures under high temperatures; low molecular weight components have poor thermal stability and are prone to volatilization at high temperatures. Furthermore, a low degree of condensation makes it difficult to form hard carbon microcrystals with long-range disorder and short-range order; instead, it tends to form graphite-like microregions or numerous disordered defects, which is detrimental to the reversible storage of sodium ions.

[0004] Hard carbon materials prepared by direct carbonization of traditional asphalt suffer from problems such as uncontrollable microstructure, underdeveloped closed-pore structure, and uneven heteroatom doping, resulting in sodium storage performance, especially plateau capacity and first coulombic efficiency, that fail to meet commercial requirements. Existing technologies mainly improve the performance of asphalt-based hard carbon through pre-oxidative crosslinking or modification with additives. However, these methods are mostly based on physical crosslinking or non-selective oxidation, making it difficult to achieve precise control over the molecular structure of carbon precursors. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention utilizes a high-content component in asphalt to transform disordered asphalt molecules into a predetermined cross-linked network through a dipole cycloaddition reaction, thereby preparing a hard carbon microstructure with short-range order and long-range disorder.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing pitch-based hard carbon materials based on dipole cycloaddition reactions includes the following steps: Step 1: Take the asphalt raw material and perform Soxhlet extraction with toluene and tetrahydrofuran in sequence, and collect the tetrahydrofuran soluble component; Step 2: Mix the soluble components with aldehydes and N-alkylglycine compounds; Step 3: The reaction is carried out under heating conditions. The aldehyde compound and the N-alkylglycine compound are condensed and decarboxylated to generate 1,3-dipolar-nitromethyl ylide in situ. The nitromethyl ylide undergoes a [3+2] cycloaddition reaction with the aromatic ring in the asphalt molecule to form a pyrrolidine ring crosslinking structure, thus obtaining the modified asphalt precursor. Step 4: Carbonize the modified asphalt precursor to obtain asphalt-based hard carbon material.

[0007] Furthermore, the asphalt raw material is one or more of petroleum asphalt, coal tar pitch, and biomass asphalt.

[0008] Furthermore, the aldehyde compound is selected from one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, and furfural.

[0009] Furthermore, the N-alkylglycine compound is selected from one or more of N-methylglycine, N-ethylglycine, N-propylglycine, N-butylglycine, and N-hexylglycine.

[0010] Furthermore, the molar ratio of the aldehyde compound to the N-alkylglycine compound is 1:0.5-1:2, more preferably 1:1.

[0011] Furthermore, in step 2, the total mass of the aldehyde compound and the N-alkylglycine compound is 1-20 wt% of the mass of the soluble component, more preferably 5-15 wt%.

[0012] Furthermore, in step 2, the reaction conditions are as follows: in a closed reaction vessel, at 80-150 °C for 2-8 h, more preferably at 80-100 °C for 3-5 h.

[0013] Furthermore, the carbonization conditions in step 3 are: carbonization temperature 1000-1600°C, heating rate 2-10°C / min, and holding time 1-4 h.

[0014] The present invention further provides a pitch-based hard carbon material prepared according to the above preparation method.

[0015] The third objective of this invention is to provide an application of pitch-based hard carbon material in battery anode materials.

[0016] This invention first classifies the asphalt components, retaining only the tetrahydrofuran-soluble component (THFS) with moderate molecular structure and uniform reactivity as the reaction base. This step effectively avoids the negative interference of "volatile light components" and "graphitized heavy components" in the original asphalt, providing a highly uniform reaction environment for the subsequent dipole cycloaddition reaction. By utilizing the high content of the asphalt components, the carbonyl functional group in the aldehyde condenses with the secondary amine of glycine to generate an imine cation intermediate. Subsequently, one molecule of carbon dioxide is removed to form a strongly electrophilic 1,3-dipole. The three atoms (CNC) of the dipole combine with a C=C double bond (two atoms) in the aromatic ring to form a stable five-membered pyrrolidine ring. Therefore, asphalt molecules can be covalently linked to form a pre-crosslinked network before carbonization, suppressing excessive ordering caused by carbon atom rearrangement under high temperature conditions. In other words, through the dipole cycloaddition reaction, disordered asphalt molecules can be transformed into predetermined crosslinks, thereby preparing a hard carbon microstructure with short-range order and long-range disorder. This technology has the advantages of high reaction efficiency, mild conditions, and well-defined product structure.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. Precise Microstructure Control: A covalent cross-linked network is constructed before carbonization via a dipolar cycloaddition reaction, fully utilizing the moderately molecular weight components of the asphalt composition. This avoids excessive graphitization of macromolecular asphaltene and the overflow of low-molecular-weight substances during carbonization. It eliminates the negative interference of these two extreme components on the carbonization process, achieves cross-linking of medium-molecular-weight substances, and significantly improves the material's platform sodium storage capacity.

[0018] 2. Improved initial coulombic efficiency: The pre-crosslinked network reduces the escape of small molecules and the formation of defects during carbonization, thereby reducing irreversible capacity loss and achieving an initial coulombic efficiency of over 85%.

[0019] 3. Strong process controllability: The dipole cycloaddition reaction can achieve directional control of the final hard carbon structure by adjusting the type and amount of aldehydes and N-alkylglycine compounds (crosslinking agents), providing a new path for the large-scale preparation of high-performance pitch-based hard carbon materials. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1The diagram shows the initial charge-discharge specific capacity and coulombic efficiency of the pitch-based hard carbon material prepared in Example 1 of this invention.

[0022] Figure 2 The diagram shows the initial charge-discharge specific capacity and coulombic efficiency of the pitch-based hard carbon material prepared in Example 2 of this invention.

[0023] Figure 3 The diagram shows the initial charge-discharge specific capacity and coulombic efficiency of the pitch-based hard carbon material prepared in Example 3 of this invention.

[0024] Figure 4 The diagram shows the initial charge-discharge specific capacity and coulombic efficiency of the pitch-based hard carbon material prepared in Example 4 of this invention.

[0025] Figure 5 The diagram shows the initial charge-discharge specific capacity and coulombic efficiency of the pitch-based hard carbon material prepared in Example 5 of this invention.

[0026] Figure 6 The diagram shows the initial charge-discharge specific capacity and coulombic efficiency of the pitch-based hard carbon material prepared in Comparative Example 1 of this invention.

[0027] Figure 7 The diagram shows the initial charge-discharge specific capacity and coulombic efficiency of the pitch-based hard carbon material prepared in Comparative Example 2 of this invention.

[0028] Figure 8 This is a transmission micrograph of the pitch-based hard carbon material prepared in Example 1 of the present invention.

[0029] Figure 9 This is a transmission micrograph of the pitch-based hard carbon material prepared in Comparative Example 1 of the present invention. Detailed Implementation

[0030] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] Example 1 (1) Take 100 g of high temperature coal tar pitch and extract it sequentially with toluene and tetrahydrofuran. Collect the tetrahydrofuran soluble component (THFS) and obtain about 30 g of intermediate component after vacuum drying.

[0033] (2) Take 10g of the above THFS component, dissolve it in 80mL of N,N-dimethylformamide, add 0.5g of N-methylglycine and 0.4g of benzaldehyde (molar ratio of about 1:1), and stir to mix evenly.

[0034] (3) The mixed solution was reacted at 120°C for 3 hours. After the reaction was completed, the solvent was removed by rotary evaporation to obtain the modified asphalt precursor.

[0035] (4) The modified asphalt precursor was placed in a tube furnace and heated to 1300°C at 5°C / min under a nitrogen atmosphere and held for 2 hours to obtain asphalt-based hard carbon material.

[0036] (5) The prepared hard carbon anode material was mixed with the binder sodium carboxymethyl ester (CMC), conductive carbon black, and styrene-butadiene rubber (SBR) at a mass ratio of 94:1.5:1.5:3 to prepare a fine and uniform electrode slurry. The electrode slurry was coated onto copper foil, dried, and then cut into appropriately sized electrode sheets. A sodium-ion coin cell was assembled using commercial sodium as the counter electrode and 1M NaPF6 in DIGLYME=100Vol% as the electrolyte.

[0037] According to BET specific surface area testing, the specific surface area of ​​the hard carbon material prepared in this embodiment is 8.1927 m² / g. The prepared sodium-ion battery, after constant current charge-discharge electrochemical testing within the 0-2V operating range, exhibited a reversible specific capacity of 342.57 mAh / g at 0.1C rate and an initial coulombic efficiency of 89.32%. Figure 1 Transmission spectrum () Figure 8 This demonstrates that the hard carbon exhibits a typical long-range ordered, short-range disordered hard carbon structure, with abundant and uniformly distributed closed pores that provide suitable space for metal nanoclusters, further enhancing sodium storage capacity and plateau capacity. Therefore, this hard carbon anode material demonstrates superior sodium storage performance.

[0038] Example 2 (1) Take 100g of petroleum asphalt with a softening point of 70℃, and perform Soxhlet extraction with toluene and tetrahydrofuran in sequence, and collect about 53g of THFS component.

[0039] (2) Take 10 g of the above THFS component, dissolve it in 80 mL of dimethyl sulfoxide, add 0.5 g of N-methylglycine and 0.4 g of benzaldehyde, and stir to mix evenly.

[0040] (3) The mixed solution was reacted at 120 °C for 3 hours. After the reaction was completed, the solvent was removed by rotary evaporation to obtain the modified asphalt precursor.

[0041] (4) Same as steps (4) and (5) in Example 1.

[0042] The hard carbon material prepared in this embodiment has a specific surface area of ​​6.1605 m² / g, as tested. Electrochemical testing showed a discharge capacity of 347.28 mAh / g at 0.1C, a charge specific capacity of 297.18 mAh / g, and an initial coulombic efficiency of 85.57%. This demonstrates the successful application of ultra-low softening point asphalt in its preparation.

[0043] Example 3 (1) Take 100 g of petroleum asphalt with a softening point of 200℃, and perform Soxhlet extraction with toluene and tetrahydrofuran in sequence, and collect about 22 g of THFS component.

[0044] (2) Take 10 g of the above THFS component, dissolve it in 80 mL of dimethyl sulfoxide, add 0.5 g of N-methylglycine and 0.4 g of benzaldehyde, and stir to mix evenly.

[0045] (3) The mixed solution was reacted at 120 °C for 3 hours. After the reaction was completed, the solvent was removed by rotary evaporation to obtain the modified asphalt precursor.

[0046] (4) Same as steps (4) and (5) in Example 1.

[0047] The hard carbon material prepared in this embodiment has a specific surface area of ​​5.8327 m² / g. Electrochemical testing showed that its discharge capacity at 0.1C is 389.78 mAh / g, its reversible specific capacity is 335.52 mAh / g, and its initial coulombic efficiency is 86.08%.

[0048] Example 4 (1) Take 100g of high temperature coal tar pitch and extract it sequentially with toluene and tetrahydrofuran. Collect the tetrahydrofuran soluble component (THFS) and obtain about 30g of intermediate component after vacuum drying.

[0049] (2) Take 10g of the above THFS component, dissolve it in 80mL of N,N-dimethylformamide, add 0.5g of N-propylglycine and 0.4g of benzaldehyde (molar ratio of about 1.13:1), and stir to mix evenly.

[0050] (3) The mixed solution was reacted at 120°C for 3 hours. After the reaction was completed, the solvent was removed by rotary evaporation to obtain the modified asphalt precursor.

[0051] (4) Same as steps (4) and (5) in Example 1.

[0052] The hard carbon material prepared in Comparative Example 1 was tested and found to have a reversible specific capacity of 321.21 mAh / g and an initial coulombic efficiency of 86.07%, which is slightly lower than that in Example 1. This indicates that N-methylglycine has higher reactivity than N-propylglycine, and therefore exhibits superior performance.

[0053] Example 5 (1) Take 100g of high temperature coal tar pitch and extract it sequentially with toluene and tetrahydrofuran. Collect the tetrahydrofuran soluble component (THFS) and dry it under vacuum to obtain an intermediate component of about 30g.

[0054] (2) Take 10g of the above THFS component, dissolve it in 80mL of N,N-dimethylformamide, add 0.5g of N-methylglycine and 0.4g of formaldehyde, and stir to mix evenly.

[0055] (3) The mixed solution was reacted at 120°C for 3 hours. After the reaction was completed, the solvent was removed by rotary evaporation to obtain the modified asphalt precursor.

[0056] (4) Same as steps (4) and (5) in Example 1.

[0057] Testing showed that the reversible specific capacity of the hard carbon material prepared in Comparative Example 2 was 313.83 mAh / g, with an initial coulombic efficiency of 86.79%, slightly lower than that in Example 1. This indicates that, compared to formaldehyde, the rigid benzene rings introduced by benzaldehyde can more effectively hinder the stacking of pitch aromatic layers during carbonization, thereby forming larger interlayer spacing and more abundant closed pores.

[0058] Comparative Example 1 (1) Take 10g of the THFS component separated in step (1) of Example 1, without functionalization and crosslinking treatment, and directly perform pre-carbonization and high-temperature carbonization under the same conditions as step (4) and (5) of Example 1.

[0059] Tests showed that the reversible specific capacity of the hard carbon material prepared in Comparative Example 1 without crosslinking treatment was 112.70 mAh / g, and the initial coulombic efficiency was 75.69%. The plateau capacity was significantly lower than that in Example 1, proving that direct carbonization of coal tar pitch leads to unsuitable interlayer spacing, which is not conducive to sodium intercalation storage.

[0060] Comparative Example 2 (1) Take 10g of the THFS component separated in step (1) of Example 1, add 0.5g of N-methylglycine and 0.4g of benzaldehyde (molar ratio about 1:1), stir and mix evenly, mix by simple physical grinding, but do not heat to carry out the dipole cycloaddition reaction, directly carry out pre-carbonization and high-temperature carbonization, under the same conditions as step (4) (5) of Example 1.

[0061] The hard carbon material prepared in Comparative Example 2 was tested and found to have a reversible specific capacity of 168.12 mAh / g and an initial coulombic efficiency of 72.31%. Figure 7 The limited performance improvement indicates that physical mixing cannot form an effective covalent cross-linked network.

[0062] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing pitch-based hard carbon materials based on dipole cycloaddition reactions, characterized in that, Includes the following steps: Step 1: Take the asphalt raw material and perform Soxhlet extraction with toluene and tetrahydrofuran in sequence, and collect the tetrahydrofuran soluble component; Step 2: Mix the soluble components with aldehydes and N-alkylglycine compounds; Step 3: The reaction is carried out under heating conditions, and 1,3-dipolar particles are generated in situ and undergo cycloaddition reaction with the aromatic rings in the asphalt molecules to obtain the modified asphalt precursor. Step 4: Carbonize the modified asphalt precursor to obtain asphalt-based hard carbon material.

2. The method for preparing pitch-based hard carbon materials based on dipole cycloaddition reaction according to claim 1, characterized in that, The asphalt raw material is one or more of petroleum asphalt, coal tar pitch, and biomass asphalt.

3. The method for preparing pitch-based hard carbon material based on dipole cycloaddition reaction according to claim 1, characterized in that, The aldehyde compounds are selected from one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, and furfural.

4. The method for preparing pitch-based hard carbon material based on dipole cycloaddition reaction according to claim 1, characterized in that, The N-alkylglycine compounds are selected from one or more of N-methylglycine, N-ethylglycine, N-propylglycine, N-butylglycine, and N-hexylglycine.

5. The method for preparing pitch-based hard carbon material based on dipole cycloaddition reaction according to claim 1, characterized in that, The molar ratio of the aldehyde compound to the N-alkylglycine compound is 1:0.5-1:

2.

6. The method for preparing pitch-based hard carbon material based on dipole cycloaddition reaction according to claim 1, characterized in that, In step 2, the total mass of aldehydes and N-alkylglycine compounds is 1-20 wt% of the mass of the soluble components.

7. The method for preparing pitch-based hard carbon material based on dipole cycloaddition reaction according to claim 1, characterized in that, In step 2, the reaction conditions are as follows: in a closed reaction vessel, at 80-150 °C, for 2-8 h.

8. The method for preparing pitch-based hard carbon material based on dipole cycloaddition reaction according to claim 1, characterized in that, The carbonization conditions in step 3 are: carbonization temperature 1000-1600°C, heating rate 2-10°C / min, and holding time 1-4 h.

9. A pitch-based hard carbon material prepared by any one of claims 1-8.

10. The application of the pitch-based hard carbon material as described in claim 9 in battery anode materials.

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