Preparation method and application of asphalt-based carbon material

Abstract

The invention discloses a preparation method and application of an asphalt-based carbon material, and belongs to the technical field of preparation of carbon materials. The preparation method of the asphalt-based carbon material comprises the following steps: carrying out low-temperature heat treatment on biomass to obtain pretreated biomass; mixing asphalt, the pretreated biomass and an activating agent, and activating to obtain the asphalt-based carbon material. Dependence on a special template agent is abandoned, and the method which is simple in technological process, highly repeatable in result, convenient and fast to operate and quite suitable for large-scale industrial production is adopted. The asphalt-based carbon material prepared by the method shows excellent performance, is particularly suitable for manufacturing an electrode material of a supercapacitor, can remarkably improve the energy density and the cycling stability of the supercapacitor, and brings an innovative breakthrough to the field of high-power energy storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of carbon materials, and more specifically relates to a preparation method and application of a pitch-based carbon material. Background Art

[0002] Asphalt and biomass are commonly used raw materials in the preparation of electrode materials. Asphalt contains a large number of polycyclic aromatic hydrocarbons and polynuclear aromatic hydrocarbon structural units, has a high degree of graphitization, is not easy to form pores, and has few active sites. Biomass precursors contain layered porous structures and rich heteroatoms, have many active sites, but exhibit low conductivity. The addition of biomass can solve the expansion problem of asphalt during carbonization, and the advantages of asphalt and biomass can be complemented by mixing and co-carbonizing.

[0003] The common asphalt and biomass are used together to prepare electrode materials, which usually require special templates to increase the specific surface area and porosity of the electrode materials, thereby improving the electrochemical properties of the electrode materials, and increasing the charge and discharge capacity and cycle stability of the electrode materials. In addition, in order to avoid volume deformation and structural collapse of the electrode materials during the charge and discharge process, it is necessary to add support materials (such as MXene) to alleviate structural collapse and improve the cycle stability of the electrode materials. The preparation process of the above common electrode materials needs to rely on special templates and external support materials, and the preparation process is complicated, which limits its development in the field of high-power energy storage. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a pitch-based carbon material and its application, so as to solve the problems existing in the above-mentioned prior art and realize the preparation of a pitch-based carbon material with a simple process flow, highly repeatable results, convenient operation and very suitable for large-scale industrial production.

[0005] To achieve the above object, the present invention provides the following solutions: One of the technical solutions of the present invention is to provide a method for preparing a pitch-based carbon material, comprising the following steps: The biomass is subjected to low temperature heat treatment to obtain pretreated biomass; the asphalt, the pretreated biomass and an activator are mixed and activated to obtain an asphalt-based carbon material.

[0006] The present invention abandons the reliance on special templates and adopts a method with a simple process flow, highly repeatable results, convenient operation and very suitable for large-scale industrial production. The present invention adopts a two-step method, namely, first subjecting the biomass to low-temperature heat treatment and then mixing it with asphalt for co-carbonization to prepare asphalt-based carbon material; the biomass after low-temperature heat treatment contains less volatile matter and tar, and forms a certain coke structure during the low-temperature heat treatment process, which reduces the influx of molten colloid into the asphalt skeleton when it is subsequently mixed with asphalt. At the same time, during the co-carbonization process, the molten asphalt can flow into the carbon skeleton of the biomass that has been subjected to low-temperature heat treatment, thereby playing a certain supporting role for the carbon skeleton of the biomass, making it less likely to collapse, solving the limitation problem that the structural support of conventional electrode materials needs to rely on external supporting materials (such as MXene); and the addition of biomass can solve the expansion problem of asphalt during the carbonization process, improve the stability of the obtained electrode material, and further improve the cycle stability of the supercapacitor; The present invention increases the carbon content in the pretreated biomass by low-temperature heat treatment of biomass, and releases a large amount of volatiles in the biomass during the low-temperature heat treatment process, so that the carbon material produces an initial pore structure, which is co-carbonized with asphalt to obtain an electrode material with the advantages of a porous structure, a large specific surface area, and a high porosity. The problem of blockage of ion transport channels caused by improper pore structure matching of conventional carbon materials is solved, the transmission efficiency of electrolyte ions is improved, and the electrochemical performance of carbon materials is improved, which is of great significance.

[0007] Optionally, the biomass includes one or more of edamame, cotton, needles, watermelon rind, nut shells, seaweed and coconut shells; the present invention has no special limitation on the type of biomass, as long as it is the biomass used in the preparation of electrode materials.

[0008] Preferably, the low temperature heat treatment is carried out in an inert atmosphere, the temperature of the low temperature heat treatment is 250-550° C., and the time of the low temperature heat treatment is 20-100 min; the inert atmosphere includes but is not limited to nitrogen.

[0009] The present invention can ensure the appropriate porosity and pore structure of the asphalt-based carbon material by controlling the temperature and time of the low-temperature heat treatment; exceeding the upper limit of the temperature and time will cause deformation and densification of the pore structure, and reduce the miscibility with asphalt; below the lower limit of the temperature and time, the pore structure will be incompletely developed and more volatile matter will remain.

[0010] Optionally, the asphalt is coal tar; and the activator comprises potassium hydroxide.

[0011] Preferably, the mass ratio of the pretreated biomass to the asphalt is 1:1-4; the mass ratio of the total mass of the pretreated biomass and the asphalt to the activator is 1:3-5.

[0012] The present invention can prepare a carbon material with relatively rich specific surface area and pore structure by controlling the mass ratio of asphalt and pretreated biomass; if the dosage is higher than this dosage range, the surface functional group content and pore structure of the final carbon material will be poor, thereby affecting the electrochemical properties of the electrode material; if the dosage is lower than this dosage range, the final carbon material will be affected by the increase in the proportion of biomass added, resulting in enhanced reaction activity with the activator, which in turn leads to serious pore structure defects, thereby enhancing the transfer resistance of the charge during the transmission process.

[0013] Preferably, the particle size of the pretreated biomass is 60-200 mesh.

[0014] Preferably, the mixing time is 120-160 min; the activation treatment is carried out in a nitrogen atmosphere, using an activator potassium hydroxide for activation, the activation treatment temperature is 700-1000° C., the activation treatment heating rate is 5-8° C. / min, and the activation treatment insulation time is 60-120 min.

[0015] Preferably, after the activation treatment, the method further comprises washing the obtained product to neutrality.

[0016] The second technical solution of the present invention is to provide a pitch-based carbon material prepared according to the above-mentioned preparation method.

[0017] The third technical solution of the present invention is to provide an application of the above-mentioned asphalt-based carbon material in the preparation of supercapacitors.

[0018] A fourth technical solution of the present invention provides a supercapacitor, wherein the electrode material of the supercapacitor is the above-mentioned asphalt-based carbon material.

[0019] The present invention discloses the following technical effects: (1) The present invention abandons the reliance on special templates and adopts a method with simple process flow, highly repeatable results, convenient operation and very suitable for large-scale industrial production. The pitch-based carbon material prepared by this method exhibits excellent performance and is particularly suitable for the manufacture of electrode materials for supercapacitors. It can significantly improve the energy density and cycle stability of supercapacitors, bringing innovative breakthroughs to the field of high-power energy storage; (2) The present invention successfully prepares a pitch-based carbon material with a well-developed pore structure, high porosity, large specific surface area, multiple active sites, and rich in various functional groups through a two-step method, namely, low-temperature heat treatment of biomass (pre-carbonization) and activation (co-carbonization, activation) after mixing with asphalt. When used as an electrode material for supercapacitors, it exhibits excellent electrochemical properties, good cycle stability, and excellent rate performance; (3) The present invention has the advantages of abundant raw material sources, simple method, low preparation cost, resource friendliness, and easy practical application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The specific capacitance diagram of the pitch-based carbon material obtained in Examples 1 to 3; Figure 2 The specific capacitance diagram of the porous carbon material obtained in Comparative Examples 1 to 4; Figure 3 The nitrogen adsorption and desorption diagrams and pore size distribution diagrams of the materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4, wherein (a) is a nitrogen adsorption and desorption diagram, and (b) is a pore size distribution diagram; Figure 4 The specific surface area and pore volume of the materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4 are shown in FIG. Figure 5 The characterization results of the surface chemical composition of the pitch-based carbon materials obtained in Examples 1 to 3; Figure 6 It is the GCD curve diagram of the materials obtained in Examples 1-3 and Comparative Examples 1-4. DETAILED DESCRIPTION

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0022] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0023] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0024] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0025] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0026] The biomass used in the following examples and comparative examples is a product or by-product of agricultural production and processing, and coal tar is a by-product of the dry distillation process of coal and the coking industry, all of which are obtained by conventional material collection methods.

[0027] Example 1 100g of edamame powder was placed in a reactor and heat treated at a stirring speed of 100r / s. Before heating, nitrogen was purged to replace the air in the reaction vessel, and then the temperature was set to 350℃, the constant temperature time was 30min, and then the pretreated edamame with a particle size of 160-200 mesh was obtained by grinding. The pretreated edamame and coal tar were fully mixed in a mass ratio of 1:2, and potassium hydroxide was added thereto to ensure that the mass ratio of the mixed mixture to potassium hydroxide was 1:5, and the mixture was placed in a stirrer and stirred for 140min to stir evenly. The obtained mixture was placed in a rotary tube furnace in a nitrogen atmosphere and activated at a constant temperature of 700℃ for 90min, with a heating rate of 5℃ / min. The obtained product was washed with 1M hydrochloric acid solution and deionized water until neutral, and then dried in a vacuum drying oven for 8h to obtain a pitch-based carbon material.

[0028] Example 2 100g of cotton was placed in a reactor and heat treated at a stirring speed of 100r / s. Before heating, nitrogen was purged to replace the air in the reaction vessel, and then the temperature was set to 450℃, the constant temperature time was 60min, and then the pretreated cotton with a particle size of 120-180 mesh was obtained by grinding. The pretreated cotton and coal tar were fully mixed in a mass ratio of 1:1, and potassium hydroxide was added thereto to ensure that the mass ratio of the mixed mixture and potassium hydroxide was 1:3, and the mixture was placed in a stirrer and stirred for 150min to stir evenly. The obtained mixture was placed in a rotary tube furnace in a nitrogen atmosphere and activated at a constant temperature of 1000℃ for 60min, with a heating rate of 6℃ / min. The obtained product was washed with 1M hydrochloric acid solution and deionized water until neutral, and then dried in a vacuum drying oven for 8h to obtain a pitch-based carbon material.

[0029] Example 3 100g of needles were placed in a reactor and heat treated at a stirring speed of 100r / s. Before heating, nitrogen was used to purge the air in the reaction vessel, and then the temperature was set to 550°C for 90 minutes. After grinding, pretreated needles with a particle size of 60-120 mesh were obtained. The pretreated needles and coal tar were fully mixed at a mass ratio of 1:3, and potassium hydroxide was added thereto to ensure that the mass ratio of the mixed mixture to potassium hydroxide was 1:1, and the mixture was placed in a stirrer and stirred for 160 minutes to stir evenly. The obtained mixture was placed in a rotary tube furnace in a nitrogen atmosphere and activated at a constant temperature of 900°C for 120 minutes, with a heating rate of 8°C / min. The obtained product was washed with 1M hydrochloric acid solution and deionized water until neutral, and then dried in a vacuum drying oven for 8 hours to obtain an asphalt-based carbon material.

[0030] The performance of the asphalt-based carbon materials obtained in Examples 1 to 3 was tested, and the results were as follows: Figure 1 shown.

[0031] Figure 1 Specific capacitance diagram of the pitch-based carbon material obtained in Examples 1 to 3. Figure 1 It can be seen that the asphalt-based carbon material obtained in Example 1 has a specific capacitance of 434F / g at a current of 0.5A / g. When the current density increases to 20A / g, the specific capacity of the electrode material can still reach 322F / g, and can maintain 74.2% of the initial capacity. The asphalt-based carbon material obtained in Example 2 has a specific capacity of 485F / g at a current density of 0.5A / g. When the current density increases to 20A / g, the specific capacity of the electrode material can still reach 359F / g, and can maintain 74.0% of the initial capacity. The asphalt-based carbon material obtained in Example 3 has a specific capacity of 285F / g at a current density of 0.5A / g. When the current density increases to 20A / g, the specific capacity of the electrode material can still reach 191F / g, and can maintain 67.0% of the initial capacity. It shows that the asphalt-based carbon material obtained by the present invention has good cycle stability and high specific capacitance.

[0032] Comparative Example 1 100g of coal tar was placed in a reactor and heat treated at a stirring speed of 100r / s. Before heating, nitrogen was used to purge the air in the reaction vessel, and then the temperature was set to 350°C for 80min. The pretreated coal tar and potassium hydroxide were placed in a stirrer at a mass ratio of 1:3 and stirred for 140min. The resulting mixture was placed in a rotary tube furnace in a nitrogen atmosphere and activated at a constant temperature of 800°C for 60min, with a heating rate of 5°C / min. The resulting product was washed with 1M hydrochloric acid solution and deionized water until neutral, and then dried in a vacuum drying oven for 8h to obtain a porous carbon material.

[0033] Comparative Example 2 The difference from Comparative Example 1 is that "coal tar" is replaced by "edamame", and the rest is the same as Comparative Example 1.

[0034] Comparative Example 3 The difference from Comparative Example 1 is that "coal tar" is replaced by "cotton", and the rest is the same as Comparative Example 1.

[0035] Comparative Example 4 The difference from Comparative Example 1 is that "coal tar pitch" is replaced by "needle leaf", and the rest is the same as Comparative Example 1.

[0036] Figure 2 The specific capacitance diagram of the porous carbon material obtained in Comparative Examples 1 to 4. Figure 1 and Figure 2 From the comparison of data, it can be seen that Example 1, Example 2 and Example 3 all show good electrochemical properties, especially at low current density, the specific capacitance is higher. When the current density is 0.5A / g, the specific capacitance of the materials obtained in Example 1, Example 2, Example 3 and Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 are 434F / g, 485F / g, 285F / g, 278F / g, 248F / g, 215F / g, 287F / g respectively; when the current density is 20A / g, the specific capacitance of the materials obtained in Example 1, Example 2, Example 3 and Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 are 322F / g, 359F / g, 191F / g, 193F / g, 140F / g, 113F / g, 220F / g respectively. It can be seen that the specific capacitance of the material obtained in the embodiment is higher than that of the material obtained in the comparative example, and the asphalt-based carbon material obtained in the present invention has a higher specific capacity and capacity retention rate.

[0037] Comparative Example 5 The difference from Example 1 is that the step of low-temperature heat treatment of edamame is omitted, and the rest is the same as Example 1.

[0038] The porous carbon material obtained in Comparative Example 5 was subjected to performance testing. The test showed that at a current of 0.5 A / g, the specific capacitance of the material was 268 F / g. When the current density increased to 20 A / g, the specific capacitance of the material reached 177 F / g, and 66% of the initial capacitance could be maintained.

[0039] Comparative Example 6 The difference from Example 1 is that the temperature of the low-temperature heat treatment is adjusted from 350° C. to 750° C., and the rest is the same as Example 1.

[0040] The porous carbon material obtained in Comparative Example 6 was subjected to performance testing. The test showed that at a current of 0.5 A / g, the specific capacitance of the material was 275 F / g. When the current density increased to 20 A / g, the specific capacitance of the material reached 176 F / g, and 64% of the initial capacitance could be maintained.

[0041] Comparative Example 7 The difference from Example 1 is that the temperature of the low-temperature heat treatment is adjusted from 350° C. to 150° C., and the rest is the same as Example 1.

[0042] The porous carbon material obtained in Comparative Example 7 was subjected to performance testing. The test showed that at a current of 0.5 A / g, the specific capacitance of the material was 259 F / g. When the current density increased to 20 A / g, the specific capacitance of the material reached 162 F / g, and 62.5% of the initial capacitance could be maintained.

[0043] Depend on Figure 1 It can be seen from the test results of comparative examples 5 to 7 that the asphalt-based carbon material obtained in the present invention has higher specific capacity and capacity retention rate.

[0044] The pore structures of the materials obtained from test examples 1 to 3 and comparative examples 1 to 4 are as follows: The specific surface area and pore structure of the prepared materials were measured using a N2 physical adsorption instrument (ASAP2460, USA). The specific surface area, micropore specific surface area, micropore volume, and total pore volume of the samples were calculated using the BET (Brunauer-Emmett-Teller), t-Plot, and BJH (Barrett-Joyner-Halenda) methods, respectively; the mesopore volume is the total pore volume minus the micropore volume, and the pore size distribution is determined using the DFT (Density Functional Theory) method. The results are shown in Figure 3 and Figure 4 shown.

[0045] Figure 3 The nitrogen adsorption and desorption diagrams and pore size distribution diagrams of the materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4, wherein (a) is a nitrogen adsorption and desorption diagram, and (b) is a pore size distribution diagram; Figure 4 The specific surface area and pore volume of the materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4 are shown in FIG. Figure 4 In the figure, the bars correspond to the specific surface area, and the black solid boxes correspond to the pore volume.

[0046] from Figure 3 and Figure 4 The results show that the specific surface areas of the materials prepared in Example 1, Example 2, and Example 3 are all higher than those of the materials prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, and the specific surface area of ​​Example 2 is as high as 3000 m 2 / g or more, the specific surface areas of the materials prepared in Comparative Examples 1, 2, 3 and 4 are generally low. In addition, the materials prepared in Examples 1, 2 and 3 all have a multi-level pore structure (such as 0.5-1 nm, 1-2 nm, 2-3 nm, 16 or 40 nm or more), and their micropores account for a high proportion. The micropore volume / total pore volume of Example 2 is more than 20. The N2 adsorption results show that the pitch-based carbon material prepared by the present invention has the advantages of a porous structure, a large specific surface area and the like.

[0047] The surface chemical composition of the pitch-based carbon materials obtained in Examples 1 to 3 was characterized: X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha+) was used to characterize the chemical composition of the surface of the pitch-based carbon materials obtained in Examples 1 to 3. This information was provided by measuring the energy distribution of photoelectrons emitted from the sample surface. The results are shown in Figure 2. Figure 5 shown.

[0048] Figure 5 These are the characterization results of the surface chemical composition of the pitch-based carbon materials obtained in Examples 1 to 3.

[0049] Depend on Figure 5 It can be seen that with the introduction of biomass and the interaction between biomass and asphalt under the action of the activator, the asphalt-based carbon materials prepared in Examples 1, 2, and 3 have oxygen-containing functional groups (CO, C=O, and -OH in the oxygen-containing spectrum peak range) and nitrogen-containing functional groups (pyridinic nitrogen, pyrrolic nitrogen, etc. in the nitrogen-containing spectrum peak range), etc. This proves that the surface of the asphalt-based carbon material prepared by the present invention contains multiple functional groups.

[0050] Figure 6 It is the GCD curve diagram of the materials obtained in Examples 1-3 and Comparative Examples 1-4.

[0051] Depend on Figure 6 It can be seen that at a current of 0.5 A / g, the materials prepared in Example 1, Example 2, Example 3 and Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 all show a typical nearly isosceles triangle GCD curve, which reflects the capacitance behavior of the double electric layer as electrodes during the charge and discharge process. Compared with Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, the GCD curves of Example 1, Example 2, and Example 3 show slight asymmetry, which is related to the addition of biomass, proving that heteroatom functional groups are successfully introduced under the method of the present invention, and these functional groups can provide more charge storage sites, thereby improving the electrochemical performance of the material.

[0052] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0053] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a pitch-based carbon material, characterized in that: The steps include: The biomass is subjected to low temperature heat treatment to obtain pretreated biomass; the asphalt, the pretreated biomass and an activator are mixed and activated to obtain an asphalt-based carbon material.

2. The preparation method according to claim 1, characterized in that: The biomass includes one or more of edamame, cotton, needles, watermelon rind, nut shells, seaweed and coconut shells.

3. The preparation method according to claim 1, characterized in that: The low temperature heat treatment is carried out in an inert atmosphere, the temperature of the low temperature heat treatment is 250-550° C., and the time of the low temperature heat treatment is 20-100 minutes.

4. The preparation method according to claim 1, characterized in that: The asphalt is coal tar; and / or the activator includes potassium hydroxide; and / or the mass ratio of the pretreated biomass to the asphalt is 1:1-4; and / or the mass ratio of the total mass of the pretreated biomass and asphalt to the activator is 1:3-5.

5. The preparation method according to claim 1, characterized in that: The particle size of the pretreated biomass is 60-200 meshes.

6. The preparation method according to claim 1, characterized in that: The mixing time is 120-160 min; and / or, the activation treatment is carried out in a nitrogen atmosphere, the activation treatment temperature is 700-1000° C., the activation treatment heating rate is 5-8° C. / min, and the activation treatment holding time is 60-120 min.

7. The preparation method according to claim 1, characterized in that: After the activation treatment, the method further comprises the step of washing the obtained product to neutrality.

8. A pitch-based carbon material prepared according to the preparation method according to any one of claims 1 to 7.

9. Use of the pitch-based carbon material according to claim 8 in preparing a supercapacitor.

10. A supercapacitor, characterized in that: The electrode material of the supercapacitor is the pitch-based carbon material according to claim 8.

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