Preparation Method and Application of an Asphalt-Based Carbon Material

Abstract

The present invention discloses a preparation method and application of an asphalt-based carbon material, belonging to the technical field of carbon material preparation. The preparation of the asphalt-based carbon material comprises the following steps: performing low-temperature heat treatment on biomass to obtain pretreated biomass; mixing asphalt, pretreated biomass and an activator and then performing activation treatment to obtain the asphalt-based carbon material. The present invention abandons the dependence on special templating agents and adopts a method with a simple process flow, highly repeatable results, convenient operation and very suitable for large-scale industrial production. The asphalt-based carbon material prepared by this method exhibits excellent properties, is particularly suitable for manufacturing electrode materials of supercapacitors, can significantly improve the energy density and cycle stability of supercapacitors, 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 the preparation of carbon materials, and more specifically relates to a preparation method and application of pitch-based carbon materials. Background Art

[0002] Pitch and biomass are commonly used raw materials in the preparation of electrode materials. Since pitch contains a large number of polycyclic aromatic hydrocarbons and polynuclear aromatic hydrocarbon structural units, it has a high degree of graphitization, is not easy to form pores, and has few active sites. Biomass precursors contain a hierarchical porous structure and abundant heteroatoms, with many active sites, but exhibit low electrical conductivity. Moreover, the addition of biomass can solve the swelling problem of pitch during carbonization, and the advantages can be complementary by co-carbonizing pitch and biomass.

[0003] Commonly, the preparation of electrode materials by combining pitch and biomass usually requires special templating agents to increase the specific surface area and porosity of the electrode materials, thereby improving the electrochemical performance of the electrode materials and increasing the charge-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-discharge process, it is necessary to add a support material (such as MXene) to relieve the structural collapse and improve the cycle stability of the electrode materials. The preparation process of the above common electrode materials relies on special templating agents and externally added support materials, and the preparation process is complex, 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 preparation method and application of pitch-based carbon materials to solve the problems existing in the above-mentioned prior art, and to realize the preparation of pitch-based carbon materials with a simple process flow, highly repeatable results, convenient operation and very suitable for large-scale industrial production.

[0005] To achieve the above purpose, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention: Provide a preparation method of pitch-based carbon materials, including the following steps:

[0007] Perform low-temperature heat treatment on biomass to obtain pretreated biomass; mix pitch, pretreated biomass and an activator, and then perform activation treatment to obtain pitch-based carbon materials.

[0008] The present invention abandons the dependence on special templating agents 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 uses a two-step method, that is, first subject the biomass to low-temperature heat treatment and then co-carbonize it with pitch to prepare a pitch-based carbon material; the biomass after low-temperature heat treatment contains less volatile matter and tar, and a certain coke structure is formed during the low-temperature heat treatment process. When it is mixed with pitch later, the inflow of molten colloid into the pitch skeleton is reduced. At the same time, during the co-carbonization process, the molten pitch can flow into the carbon skeleton of the biomass after low-temperature heat treatment, thereby playing a certain supporting role in the carbon skeleton of the biomass and making it not easy to collapse, solving the problem that the structural support of conventional electrode materials needs to rely on external support materials (such as MXene); and the addition of biomass can solve the expansion problem of pitch during carbonization, improve the stability of the obtained electrode material, and further improve the cycle stability of the supercapacitor;

[0009] The present invention increases the carbon content in the pretreated biomass by low-temperature heat treatment of the biomass, and a large amount of volatile matter in the biomass is released during the low-temperature heat treatment process, so that the carbon material generates an initial pore structure. By co-carbonizing it with pitch, an electrode material with advantages such as a porous structure, a large specific surface area, and a high porosity is prepared, solving the problem of blockage of ion transport channels caused by improper pore structure matching of conventional carbon materials, improving the transport efficiency of electrolyte ions, and being of great significance for improving the electrochemical performance of carbon materials.

[0010] Optionally, the biomass includes one or more of soybeans, cotton, conifers, watermelon rinds, nut shells, seaweeds 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.

[0011] 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.

[0012] The present invention can ensure a suitable porosity and pore structure of the pitch-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 a decrease in the compatibility with pitch; below the lower limit of the temperature and time, the pore structure will not develop completely and there will be more residual volatile matter.

[0013] Optionally, the pitch is coal pitch; the activator includes potassium hydroxide.

[0014] Preferably, the mass ratio of the pretreated biomass to the pitch is 1:1~4; the mass ratio of the total mass of the pretreated biomass and the pitch to the activator is 1:3~5.

[0015] By controlling the mass ratio of asphalt and pretreated biomass, the present invention can prepare carbon materials with relatively rich specific surface area and pore structure; exceeding this dosage range will result in poor surface functional group content and pore structure of the final carbon material, thus affecting the electrochemical performance of the electrode material; below this dosage range, the final carbon material will have an enhanced reaction activity with the activator due to the increasing proportion of biomass added, leading to serious defects in the pore structure, and thus enhancing the charge transfer resistance during the transmission process.

[0016] Preferably, the particle size of the pretreated biomass is 60 - 200 mesh.

[0017] Preferably, the mixing time is 120 - 160 min; the activation treatment is carried out in a nitrogen atmosphere, using potassium hydroxide as the activator for activation, the activation temperature is 700 - 1000 °C, the heating rate of the activation treatment is 5 - 8 °C / min, and the holding time of the activation treatment is 60 - 120 min.

[0018] Preferably, after the activation treatment, it further includes the step of washing the obtained product to neutral.

[0019] The second technical solution of the present invention: Provide an asphalt-based carbon material prepared by the above preparation method.

[0020] The third technical solution of the present invention: Provide an application of the above asphalt-based carbon material in the preparation of supercapacitors.

[0021] The fourth technical solution of the present invention: Provide a supercapacitor, wherein the electrode material of the supercapacitor is the above asphalt-based carbon material.

[0022] The present invention discloses the following technical effects:

[0023] (1) The present invention abandons the dependence on special templating agents and adopts a method with a simple process flow, highly repeatable results, convenient operation and very suitable for large-scale industrial production. The asphalt-based carbon material prepared by this method exhibits excellent performance, is particularly suitable for the manufacture of electrode materials for supercapacitors, can significantly improve the energy density and cycle stability of supercapacitors, and brings an innovative breakthrough to the high-power energy storage field;

[0024] (2) Through a two-step method, namely low-temperature heat treatment of biomass (pre-carbonization) and activation after mixing with asphalt (co-carbonization, activation), the present invention successfully prepares an asphalt-based carbon material with a developed pore structure, high porosity, large specific surface area, many active sites and rich in various functional groups. When used as the electrode material of a supercapacitor, it exhibits excellent electrochemical performance, and has good cycle stability and excellent rate performance;

[0025] (3) The present invention has the advantages of rich raw material sources, simple method, low preparation cost, resource friendliness, and convenience for practical application. DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the specific capacitance diagram of the pitch-based carbon materials obtained in Examples 1 to 3;

[0027] Figure 2 It is the specific capacitance diagram of the porous carbon materials obtained in Comparative Examples 1 to 4;

[0028] Figure 3 It is the nitrogen adsorption / desorption isotherm and pore size distribution diagram of the materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4. Among them, (a) is the nitrogen adsorption / desorption isotherm, and (b) is the pore size distribution diagram;

[0029] Figure 4 It is the specific surface area and pore volume diagram of the materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4;

[0030] Figure 5 It is the characterization result of the surface chemical composition of the pitch-based carbon materials obtained in Examples 1 to 3;

[0031] Figure 6 It is the GCD curve diagram of the materials obtained in Examples 1 to 3 and Comparative Examples 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0032] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0033] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Among any stated value or range of values, the intermediate value, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0034] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can 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 related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0035] 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.

[0036] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0037] 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.

[0038] Example 1

[0039] 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.

[0040] Example 2

[0041] 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.

[0042] Example 3

[0043] 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.

[0044] 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.

[0045] 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.

[0046] Comparative Example 1

[0047] Place 100 g of coal tar pitch in a reaction kettle and conduct heat treatment under the condition that the stirring speed is 100 r / s. Before heating up, use nitrogen purge to displace the air in the reaction vessel, then set the temperature to 350 °C and the constant temperature time to 80 min. Take the pretreated coal tar pitch and potassium hydroxide in a mass ratio of 1:3 and place them in a stirrer to stir for 140 min. Place the obtained mixture in a rotary tube furnace under a nitrogen atmosphere and activate it at a constant temperature of 800 °C for 60 min, with a heating rate of 5 °C / min. Wash the obtained product with 1 M hydrochloric acid solution and deionized water until neutral, and then dry it in a vacuum drying oven for 8 h to obtain a porous carbon material.

[0048] Comparative Example 2

[0049] The difference from Comparative Example 1 is that "coal tar pitch" is replaced with "edamame", and the others are the same as Comparative Example 1.

[0050] Comparative Example 3

[0051] The difference from Comparative Example 1 is that "coal tar pitch" is replaced with "cotton", and the others are the same as Comparative Example 1.

[0052] Comparative Example 4

[0053] The difference from Comparative Example 1 is that "coal tar pitch" is replaced with "coniferous leaves", and the others are the same as Comparative Example 1.

[0054] Figure 2 It is the specific capacitance diagram of the porous carbon materials obtained in Comparative Examples 1 to 4. From Figure 1 and Figure 2 By comparing the data, it can be seen that Examples 1, 2, and 3 all show good electrochemical performance, especially with a relatively high specific capacitance at low current densities. When the current density is 0.5 A / g, the specific capacitances of the materials obtained in Examples 1, 2, 3 and Comparative Examples 1, 2, 3, 4 are 434 F / g, 485 F / g, 285 F / g, 278 F / g, 248 F / g, 215 F / g, 287 F / g respectively; when the current density is 20 A / g, the specific capacitances of the materials obtained in Examples 1, 2, 3 and Comparative Examples 1, 2, 3, 4 are 322 F / g, 359 F / g, 191 F / g, 193 F / g, 140 F / g, 113 F / g, 220 F / g respectively. It can be seen that the specific capacitance of the materials obtained in the examples is higher than that of the materials obtained in the comparative examples, and the pitch-based carbon materials obtained in the present invention have higher specific capacity and capacity retention rate.

[0055] Comparative Example 5

[0056] The difference from Example 1 is that the step of low-temperature heat treatment of edamame is omitted, and the others are the same as Example 1.

[0057] The performance of the porous carbon material obtained in Comparative Example 5 was tested. The test results showed that at a current of 0.5 A / g, the specific capacitance of this material was 268 F / g. When the current density increased to 20 A / g, the specific capacity of this material reached 177 F / g, maintaining 66% of the initial capacity.

[0058] Comparative Example 6

[0059] The difference from Example 1 was that the temperature of the low-temperature heat treatment was adjusted from 350 °C to 750 °C, and the others were the same as in Example 1.

[0060] The performance of the porous carbon material obtained in Comparative Example 6 was tested. The test results showed that at a current of 0.5 A / g, the specific capacitance of this material was 275 F / g. When the current density increased to 20 A / g, the specific capacity of this material reached 176 F / g, maintaining 64% of the initial capacity.

[0061] Comparative Example 7

[0062] The difference from Example 1 was that the temperature of the low-temperature heat treatment was adjusted from 350 °C to 150 °C, and the others were the same as in Example 1.

[0063] The performance of the porous carbon material obtained in Comparative Example 7 was tested. The test results showed that at a current of 0.5 A / g, the specific capacitance of this material was 259 F / g. When the current density increased to 20 A / g, the specific capacity of this material reached 162 F / g, maintaining 62.5% of the initial capacity.

[0064] From Figure 1 and the test results of Comparative Examples 5-7, it can be seen that the asphalt-based carbon material obtained in this invention has higher specific capacity and capacity retention rate.

[0065] The pore structures of the materials obtained in Test Examples 1-3 and Comparative Examples 1-4 were tested:

[0066] 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 by the BET (Brunauer-Emmett-Teller), t-Plot, and BJH (Barrett-Joyner-Halenda) methods, respectively; the mesopore volume was the total pore volume minus the micropore volume, and the pore size distribution was determined by the DFT (Density Functional Theory) method. The results are as Figure 3 and Figure 4 shown.

[0067] Figure 3Nitrogen adsorption - desorption isotherms and pore size distribution diagrams of the materials obtained in Examples 1 - 3 and Comparative Examples 1 - 4, where (a) is the nitrogen adsorption - desorption isotherm and (b) is the pore size distribution diagram; Figure 4 Specific surface area and pore volume diagrams of the materials obtained in Examples 1 - 3 and Comparative Examples 1 - 4. In Figure 4 it, the column chart corresponds to the specific surface area, and the black solid square corresponds to the pore volume.

[0068] From Figure 3 and Figure 4 the results, it can be seen that the specific surface areas of the materials prepared in Examples 1, 2, and 3 are all higher than those of the materials prepared in Comparative Examples 1, 2, 3, and 4. In particular, Example 2 reaches more than 3000 m 2 / g, and 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 hierarchical pore structure (such as 0.5 - 1 nm, 1 - 2 nm, 2 - 3 nm, 16 or more than 40 nm), with a high proportion of micropores. The micropore volume / total pore volume of Example 2 reaches more than 20. The N2 adsorption results can prove that the pitch - based carbon materials prepared by the present invention have advantages such as a porous structure and a large specific surface area.

[0069] Characterize the surface chemical composition of the pitch - based carbon materials obtained in Examples 1 - 3:

[0070] Use X - ray photoelectron spectroscopy (XPS, Thermo Scientific K - Alpha+) to characterize the chemical composition of the surface of the pitch - based carbon materials obtained in Examples 1 - 3. These information are provided by measuring the energy distribution of photoelectrons emitted from the sample surface. The results are as Figure 5 shown.

[0071] Figure 5 Characterization results of the surface chemical composition of the pitch - based carbon materials obtained in Examples 1 - 3.

[0072] From Figure 5 it can be seen that with the introduction of biomass and the interaction reaction between biomass and pitch under the action of the activator, the pitch - based carbon materials prepared in Examples 1, 2, and 3 have oxygen - containing functional groups (C - O, C = O, and - OH in the range of oxygen - containing spectral peaks) and nitrogen - containing functional groups (pyridine nitrogen, pyrrole nitrogen, etc. in the range of nitrogen - containing spectral peaks), etc. It is proved that the surface of the pitch - based carbon materials prepared by the present invention contains various functional groups.

[0073] Figure 6 GCD curves of the materials obtained in Examples 1 - 3 and Comparative Examples 1 - 4.

[0074] From Figure 6It 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, Comparative Example 4 all showed typical nearly isosceles triangle GCD curves, which reflected the capacitive behavior of the electric double layer during charge and discharge as electrodes. Compared with Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, the slightly asymmetric GCD curves of Example 1, Example 2, Example 3 were related to the addition of biomass, proving that heteroatom functional groups were successfully introduced under the method described in the present invention. These functional groups could provide more charge storage sites, thereby improving the electrochemical performance of the materials.

[0075] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other.

[0076] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can 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 these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Application of an asphalt-based carbon material in preparing a supercapacitor with excellent cycle stability, characterized in that, The preparation steps of the asphalt-based carbon material are as follows: Perform low-temperature heat treatment on biomass to obtain pretreated biomass; Mix asphalt, pretreated biomass and an activator, and then perform activation treatment to obtain the asphalt-based carbon material; The biomass includes one or more of young soybeans, cotton, conifers, watermelon rinds, nut shells, seaweeds and coconut shells; The low-temperature heat treatment is carried out in an inert atmosphere, the temperature of the low-temperature heat treatment is 250-450 °C, and the time of the low-temperature heat treatment is 30-60 min; The asphalt is coal tar pitch; the activator includes potassium hydroxide; 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 mass of the activator is 1:3-5; The mixing time is 120-160 min; the activation treatment is carried out in a nitrogen atmosphere, the temperature of the activation treatment is 700-1000 °C, the heating rate of the activation treatment is 5-8 °C / min, and the heat preservation time of the activation treatment is 60-120 min.

2. The application according to claim 1, characterized in that The particle size of the pretreated biomass is 60-200 mesh.

3. The application according to claim 1, wherein After the activation treatment, it further includes the step of washing the obtained product to neutral.

4. A supercapacitor, characterized in that, The electrode material of the supercapacitor is the asphalt-based carbon material in the application according to any one of claims 1-3.

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