Preparation method and application of heteroatom doped asphalt-based hard carbon

Abstract

The invention discloses a preparation method and application of heteroatom-doped asphalt-based hard carbon, and relates to the field of sodium-ion battery negative electrode materials. The preparation method comprises the following steps: mixing asphalt with a catalyst, a cross-linking agent and a solvent, and performing cross-linking modification in a reflux state to obtain a liquid precursor I; heating and pre-carbonizing the precursor I in air to obtain a precursor II; and washing the precursor II to be neutral, drying, and performing high-temperature carbonization in inert gas to obtain the heteroatom-doped asphalt-based hard carbon material. Asphalt is used as a precursor, chemical crosslinking and doping methods are used, Friedel-Crafts reaction of the asphalt is realized, and a large number of oxygen-containing functional groups and other heteroatoms are introduced. In the high-temperature carbonization process, the introduced oxygen-containing functional group and other heteroatoms can weaken or destroy the pi-pi interaction between asphalt aromatic hydrocarbons and inhibit the graphitization of asphalt of the asphalt-based carbon material, so that the carbon material forms a three-dimensional cross-linked structure, the interlayer spacing is increased, the closed pore volume is increased, and the capacity, the cycle performance and the rate capability are further improved.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to the preparation and application of a hard carbon negative electrode material for a sodium ion battery. Background Art

[0002] With the over-consumption of fossil fuels and the emergence of global environmental problems, renewable energy and even electrochemical energy storage have received increasing attention. Lithium-ion batteries dominate the world electrochemical power supply market with their advantages such as high energy density, long cycle life, and good rate performance. However, lithium batteries cannot fully meet the needs of large-scale energy storage due to insufficient lithium resources and high costs. Sodium-ion batteries have the advantages of low cost, abundant sodium reserves, and wide distribution, and are considered to be the most promising candidate for electrochemical energy storage systems.

[0003] However, the commercial application of sodium-ion batteries still lacks low-cost negative electrode materials. The development of high-performance and low-cost negative electrode materials is one of the keys to promote the commercialization of sodium-ion batteries. Asphalt is low in price and ash content. It is a mixture of petroleum residues prepared by various complex chemical reactions. It is mainly composed of a large number of polycyclic aromatic hydrocarbons and structurally related heterocyclic compounds. Direct pyrolysis of asphalt will undergo uncontrollable liquid phase carbonization to form soft carbon materials with small interlayer spacing and high orientation, resulting in poor performance of sodium-ion batteries. Studies have found that by cross-linking and modifying asphalt molecules and doping with heteroatoms to weaken or destroy the interaction between aromatic hydrocarbons, the graphitization of asphalt can be interfered with and the transformation of the microstructure can be driven. Therefore, it is of great significance to provide a low-cost preparation method and application of heteroatom-doped asphalt-based hard carbon. Summary of the invention

[0004] In order to improve the above-mentioned technical problems, one of the objects of the present invention is to provide a low-cost method for preparing heteroatom-doped asphalt-based hard carbon materials. The present invention utilizes a catalyst to catalyze the cross-linking of asphalt and cyclic organic matter, and at the same time realizes uniform doping of heteroatoms during the pre-carbonization process, thereby inhibiting the development of asphalt carbon crystallites during high-temperature carbonization and forming more disordered carbon structures. The preparation method is simple and economical.

[0005] The second object of the present invention is to provide a heteroatom-doped asphalt-based hard carbon material prepared by the above method. The cross-linked pre-carbonized asphalt-based hard carbon material has good electrochemical properties and can be used to prepare sodium ion batteries.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a heteroatom-doped pitch-based hard carbon material, the preparation method comprising the following steps:

[0008] (1) Mixing asphalt with a catalyst (which is also a heteroatom-doped precursor), a crosslinking agent and a solvent, stirring and heating the mixture under reflux to perform crosslinking modification, thereby obtaining a liquid precursor I;

[0009] (2) pre-carbonizing the precursor I by heating it in air to obtain the precursor II;

[0010] (3) washing the precursor II to neutrality and drying it, and then carbonizing it at high temperature in an inert gas to obtain a heteroatom-doped asphalt-based hard carbon material;

[0011] Preferably, the asphalt in step (1) comprises one of coal asphalt, petroleum asphalt, natural asphalt and mesophase asphalt.

[0012] Preferably, the catalyst in step (1) includes one or more of AlCl3, HCl (hydrochloric acid solution), MgCl2, ZnCl2, H2SO4 (sulfuric acid solution), H3PO4, HNO3, phytic acid, boric acid and sodium hypophosphite.

[0013] Preferably, the mass ratio of the asphalt to the catalyst in step (1) is 1:0.02-10.

[0014] Preferably, the cross-linking agent in step (1) includes one or more of tetrahydrofuran, dimethylmethane, oxalyl chloride, terephthalic acid, N-methylpyrrolidone, glucose, and zinc gluconate.

[0015] Preferably, the mass ratio of the asphalt to the solvent in step (1) is 1:0.2-50.

[0016] Preferably, the solvent in step (1) includes one or more of tetrahydrofuran, N-methylpyrrolidone, carbon tetrachloride and ethylene dichloride; when the solvent contains tetrahydrofuran and N-methylpyrrolidone, the corresponding tetrahydrofuran and N-methylpyrrolidone can be simultaneously calculated into the cross-linking agent. Further, when the cross-linking agent contains tetrahydrofuran and dimethylmethane, tetrahydrofuran and dimethylmethane are also calculated into the solvent, that is, tetrahydrofuran and dimethylmethane can be both solvent and cross-linking agent. Preferably, the mass ratio of asphalt to cross-linking agent in step (1) is 1:0.2-50.

[0017] Preferably, the cross-linking modification temperature in step (1) is 150 to 300° C., and the time is 0.1 to 24 hours.

[0018] Preferably, the pre-carbonization temperature of the precursor I in step (2) is 150-350° C., and the time is 0.1-24 h.

[0019] Preferably, the washing in step (3) is performed with deionized water and / or ethanol, and the drying time after washing to neutrality is 1 to 48 hours.

[0020] Preferably, in step (3), the high temperature carbonization temperature of the precursor II is 800-1700°C, the time is 1-12h, and the heating rate is 0.5-10°C / min;

[0021] Preferably, the inert gas in step (3) is one of nitrogen, argon and helium.

[0022] The present invention provides a heteroatom-doped asphalt-based hard carbon material prepared by the above scheme.

[0023] The present invention provides an application of a heteroatom-doped asphalt-based hard carbon material prepared by the above scheme in a sodium ion battery, especially in a negative electrode material.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The present invention provides a method for preparing a heteroatom-doped asphalt-based hard carbon material. The present invention uses asphalt as a precursor and uses a chemical crosslinking method. In the presence of a catalyst, the hydrogen atoms of the aromatic ring of the asphalt are replaced by oxygen-containing alkyl or acyl groups to generate alkyl aromatics or aromatic ketones, etc., to achieve the Friedel-Crafts reaction of the asphalt, and introduce a large number of oxygen-containing functional groups and heteroatoms in the process. Since the precursor I after the Friedel-Crafts reaction is still in a liquid state, it is conducive to uniform mixing. In the subsequent pre-carbonization process, it is conducive to the uniform doping of heteroatoms. At the same time, gas volatilization during the pre-carbonization process is conducive to the formation of a rich open pore structure of the asphalt-based carbon material. During the high-temperature carbonization process, the oxygen-containing functional groups and other heteroatoms introduced by the Friedel-Crafts reaction can weaken or destroy the π-π interaction between the asphalt aromatics, inhibit the graphitization of the asphalt of the asphalt-based carbon material, and drive the microstructure to transform into disorder, so that the carbon material forms a three-dimensional cross-linked structure with increased interlayer spacing. At the same time, the open pores shrink and close to form partially closed pores, and the closed pore volume increases, thereby improving the capacity, cycle performance and rate performance. The heteroatom-doped asphalt-based hard carbon material prepared by the present invention has a reversible specific capacity of 300 mAh g -1 The above results show that the first-cycle Coulomb efficiency is above 88%.

[0026] The raw materials used in the invention are widely available and low in cost; the preparation method is simple to operate, has a low reaction temperature, and is suitable for large-scale production.

[0027] Furthermore, in the chemical cross-linking method adopted in the present invention, the asphalt is evenly mixed with the catalyst, the cross-linking agent and the solvent, the mixed solution has good fluidity, and the Friedel-Crafts reaction can fully occur under the reflux state. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The first cycle charge and discharge test results of the S and O co-doped asphalt-based hard carbon material prepared in Example 1;

[0029] Figure 2 This is the full XPS spectrum of the S and O co-doped asphalt-based hard carbon material prepared in Example 1;

[0030] Figure 3 The cyclic performance test results of the S and O co-doped asphalt-based hard carbon material prepared in Example 1;

[0031] Figure 4 The first cycle charge and discharge test results of the S, N, O co-doped asphalt-based hard carbon material prepared in Example 2;

[0032] Figure 5 The first cycle charge and discharge test results of the P and O co-doped asphalt-based hard carbon material prepared in Example 3;

[0033] Figure 6 The first cycle charge and discharge test results of the pitch-based carbon material prepared in Comparative Example 1;

[0034] Figure 7 This is the infrared spectrum of the S and O co-doped asphalt-based hard carbon material prepared in Example 1. DETAILED DESCRIPTION

[0035] Hereinafter, the preparation method and application of the cross-linked pre-carbonized pitch-based hard carbon material of the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0036] It should be noted that "I", "II", etc. are only for the convenience of description and distinction, and cannot be understood as indicating or implying relative importance. The terms "S1", "S2", "S3", etc. used in the present invention are used to distinguish similar phenomena, and are not necessarily used to describe a specific sequence or order.

[0037] The present invention provides a method for preparing a heteroatom-doped asphalt-based hard carbon material, comprising the following steps:

[0038] S1. Mix asphalt, catalyst, cross-linking agent and solvent, stir and heat under reflux to modify, and obtain precursor I, during which heteroatoms are introduced.

[0039] S2. Pre-carbonize the precursor I by heating it in air to obtain the precursor II.

[0040] S3. After washing the precursor II to neutrality, it is carbonized at high temperature in an inert gas to obtain a pre-carbonized cross-linked asphalt material.

[0041] In step S1, the mass ratio of asphalt to catalyst can be 1:0.02-10 and uniformly mixed, preferably 1:0.5-5.

[0042] In step S1, the catalyst preferably includes one of AlCl3, HCl, MgCl2, ZnCl2, H2SO4, H3PO4, HNO3, phytic acid, boric acid and sodium hypophosphite, and more preferably H2SO4.

[0043] In step S1, the asphalt preferably includes one of coal asphalt, petroleum asphalt, natural asphalt and mesophase asphalt, and is more preferably petroleum asphalt.

[0044] In step S1, the mass ratio of the asphalt to the cross-linking agent is 1:0.2-50, and more preferably 1:5-25.

[0045] In step S1, the cross-linking agent includes one or more of tetrahydrofuran, dimethylmethane, oxalyl chloride, terephthalic acid, N-methylpyrrolidone, glucose and zinc gluconate, and is more preferably tetrahydrofuran or N-methylpyrrolidone.

[0046] In step S1, the mass ratio of the asphalt to the solvent is 1:0.2-50, and more preferably 1:5-25.

[0047] In step S1, the solvent includes one or more of tetrahydrofuran, N-methylpyrrolidone, carbon tetrachloride and ethylene dichloride.

[0048] In step S2, the pre-carbonization temperature is preferably 150-350°C, more preferably 180°C; the pre-carbonization time is preferably 0.1-24h, more preferably 1-10h.

[0049] In step S3, the drying time after washing to neutrality is preferably 1 to 48 hours, more preferably 1 to 20 hours.

[0050] In step S3, the inert gas is preferably one of nitrogen, argon and helium, and more preferably nitrogen.

[0051] In step S3, the high temperature carbonization temperature of the precursor II is 800-1700°C, and more preferably 1000-1500°C.

[0052] In step S3, the high temperature carbonization time of the precursor II is 1 to 12 hours, and more preferably 1 to 4 hours.

[0053] In step S3, the high temperature carbonization heating rate of the precursor II is 0.5-10°C / min, and more preferably 1-5°C / min.

[0054] After the high-temperature carbonization process is completed, the process is preferably cooled naturally to obtain a heteroatom-doped asphalt-based hard carbon material.

[0055] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0056] Example 1

[0057] S1. Weigh 1g of petroleum asphalt, crush it and transfer it to a three-necked flask, add 2mL of H2SO4 (concentration of 18.4mol / L), add 15mL of tetrahydrofuran, and stir at 400rpm for 30min to obtain a mixture. Then insert a straight condenser, turn on the condensing water, heat the mixture to 180℃, reflux and crosslink for 2h to obtain a liquid precursor I.

[0058] S2. Take out the precursor I, pour it into a beaker, heat it to 180°C in an oven, and pre-carbonize it for 2 hours to obtain a solid precursor II.

[0059] S3. Ball-mill the precursor II for 10 min, wash the crushed precursor II with deionized water and ethanol to neutrality, then transfer the washed and dried precursor II to a crucible, and carbonize it at 1400°C for 2 h in a tubular furnace under a nitrogen atmosphere. After natural cooling, cool it down and take it out to obtain S and O co-doped HC-1.

[0060] Example 2

[0061] The difference from Example 1 is that the tetrahydrofuran in step S1 is replaced with N-methylpyrrolidone to obtain S, N, and O co-doped HC-2.

[0062] Example 3

[0063] The difference from Example 1 is that H2SO4 in step S1 is replaced by H3PO4 (14.63 mol / L), and P and O co-doped HC-3 is obtained.

[0064] Example 4

[0065] The difference from Example 1 is that H2SO4 in step S1 is replaced with 1.138 g of boric acid to obtain B and O co-doped HC-4.

[0066] Example 5

[0067] The difference from Example 1 is that 250 mg of zinc gluconate is added in step S1 to obtain S and O co-doped HC-5.

[0068] Comparative Example 1

[0069] Weigh 1 g of asphalt, transfer the asphalt to a crucible without any treatment or modification, and carbonize it in a tubular furnace at 1400°C for 2 h under a nitrogen atmosphere. After natural cooling, take it out to obtain C-1.

[0070] Comparative Example 2

[0071] The only difference from Example 1 is that no tetrahydrofuran is added to obtain C-2.

[0072] Battery assembly and testing

[0073] The asphalt-based carbon materials, conductive carbon black, carboxymethyl cellulose and styrene-butadiene rubber prepared in different cases were mixed in a mass ratio of 90:4:3:3, deionized water (6 times the mass of hard carbon) was added to form a slurry, which was evenly coated on Cu foil and dried at 100°C for 12 hours. A 12mm circular electrode sheet was punched out from a stamping sheet as the working electrode, a metal sodium sheet was used as the counter electrode, the electrolyte was 1M NaPF6 in EC / DMC=1:1Vol%, the separator was a glass fiber separator GF / D, and a CR2032 button cell was assembled.

[0074] The prepared battery was subjected to constant current charge and discharge tests at room temperature with a voltage range of 0.001 to 2.5 V and a current density of 0.03 A g -1 The test results are shown in Table 1.

[0075] The first cycle charge and discharge curve of the pitch-based carbon material in Example 1 is as follows Figure 1 shown.

[0076] The battery prepared by the pitch-based carbon material in Example 1 was heated to 0.15A g -1 The long cycle test was carried out at a current density of Figure 3 As shown, it remains essentially unchanged after 150 laps.

[0077] Example 1 The XPS full spectrum of pitch-based carbon material is as follows Figure 2 As shown, it is proved that the material is doped with S and O elements.

[0078] Example 1 Infrared spectrum of pitch-based carbon material Figure 7 As shown, the hydrogen atoms on the aromatic hydrocarbons are replaced and oxygen-containing functional groups are introduced.

[0079] Table 1 Electrochemical data of hard carbon materials prepared in different cases

[0080]

[0081] It can be seen from Table 1 that the charging specific capacities corresponding to Examples 1-5 of the present invention are significantly higher than those corresponding to Comparative Examples 1-2. Figure 1 and Figure 6 It can be clearly seen that the 002 peak of the XRD of the cross-linked pre-carbonized asphalt-based hard carbon material prepared in Example 1 shifts to the left and has a larger peak width, which proves that its interlayer spacing increases and the microstructure transforms to disorder.

[0082] By comparing Example 1 and Comparative Example 2, it can be found that if no cross-linking agent is added in the first step, it will have a significant impact on the final battery performance.

[0083] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the spirit and scope defined by the claims, and these obvious alternative forms all belong to the protection scope of the present invention.

Claims

1. A method for preparing a heteroatom-doped pitch-based hard carbon material, characterized in that: The following steps are involved: (1) mixing asphalt with a catalyst, a crosslinking agent and a solvent, stirring and heating under reflux to perform crosslinking modification, and obtaining a liquid precursor I; (2) pre-carbonizing the precursor I by heating it in air to obtain the precursor II; (3) washing the precursor II to neutrality and drying it, and then carbonizing it at high temperature in an inert gas to obtain a heteroatom-doped asphalt-based hard carbon material; The catalyst in step (1) comprises one or more of AlCl3, HCl, MgCl2, ZnCl2, H2SO4, H3PO4, HNO3, phytic acid, boric acid and sodium hypophosphite; The cross-linking agent in step (1) includes one or more of tetrahydrofuran, dimethylmethane, oxalyl chloride, terephthalic acid, N-methylpyrrolidone, glucose, and zinc gluconate.

2. The method according to claim 1, characterized in that The asphalt in step (1) includes one of coal asphalt, petroleum asphalt, natural asphalt and mesophase asphalt.

3. The method according to claim 1, characterized in that The mass ratio of the asphalt to the catalyst in step (1) is 1:0.02-10, preferably 1:0.5-5; the mass ratio of the asphalt to the cross-linking agent in step (1) is 1:0.2-50, preferably 1:5-25; the mass ratio of the asphalt to the solvent in step (1) is 1:0.2-50, preferably 1:5-25.

4. The method according to claim 1, characterized in that The solvent in step (1) includes one or more of tetrahydrofuran, N-methylpyrrolidone, carbon tetrachloride and ethylene dichloride; when the solvent contains tetrahydrofuran and N-methylpyrrolidone, the corresponding tetrahydrofuran and N-methylpyrrolidone can be simultaneously calculated into the cross-linking agent; further, when the cross-linking agent contains tetrahydrofuran and dimethylmethane, tetrahydrofuran and dimethylmethane are also calculated into the solvent, that is, tetrahydrofuran and dimethylmethane can be both the solvent and the cross-linking agent.

5. The method according to claim 1, characterized in that The cross-linking modification temperature in step (1) is 150-300° C. and the time is 0.1-24 h.

6. The method according to claim 1, characterized in that In step (2), the pre-carbonization temperature of the precursor I is 150-350° C., and the time is 0.1-24 h.

7. The method according to claim 1, characterized in that Step (3) washing is performed using deionized water and / or ethanol; In step (3), the high temperature carbonization temperature of the precursor II is 800-1700°C, the time is 1-12h, and the heating rate is 0.5-10°C / min; The inert gas in step (3) is one of nitrogen, argon and helium.

8. A heteroatom-doped asphalt-based hard carbon material prepared according to the method described in any one of claims 1 to 7.

9. Application of the heteroatom-doped asphalt-based hard carbon material prepared by the method according to any one of claims 1 to 7 in sodium ion batteries.

10. The use according to claim 9, in particular in negative electrode materials.

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