Method for preparing graphene battery electrode from coal tar with low energy consumption

Abstract

The invention relates to the field of coal graded conversion and utilization, in particular to a method for preparing a graphene battery electrode from coal tar with low energy consumption. According to the preparation method, coal tar serves as a carbon source, graphene grows on the surface of foam metal in situ at the low temperature of 300-900 DEG C, and a graphene-metal composite substrate is formed and used for synthesizing the self-supporting electrode material; according to the preparation method, continuous production is realized by a set of continuous production system. According to the method, the energy consumption of graphene electrode production is reduced through the process of growing graphene at low temperature through coal tar, the traditional coating step is omitted, a binder and a conductive agent are not needed, and the prepared electrode shows high specific capacity and low charge transfer impedance.

Description

Technical Field

[0001] This invention relates to the field of coal graded conversion and utilization, specifically to a method for preparing graphene battery electrodes from coal tar with low energy consumption. Background Technology

[0002] Graphene, with its unique two-dimensional honeycomb lattice structure, excellent electrical conductivity, high specific surface area, and superior mechanical strength, has shown great application potential in the field of lithium-ion batteries and is considered an ideal additive for improving electrode performance. Chemical vapor deposition (CVD) is one of the commonly used techniques for preparing high-quality, large-area graphene films.

[0003] Currently, traditional CVD methods for preparing graphene typically use gaseous carbon sources such as methane and ethylene, and are carried out at reaction temperatures as high as 900°C to 1000°C. This high-temperature process places stringent requirements on equipment, consumes significant amounts of energy, and increases the production cost of graphene, thereby limiting its adoption in large-scale commercial applications such as lithium-ion batteries.

[0004] In electrode manufacturing, conventional processes typically involve mixing active materials, conductive agents (such as acetylene black), and polymer binders (such as PVDF) to form a slurry, which is then coated onto a metal current collector, followed by drying and rolling processes. This process not only introduces a large number of inactive components, reducing the active material loading and overall energy density of the electrode, but the presence of insulating binders may also increase the interfacial impedance of the electrode, adversely affecting the rate performance and cycle stability of the battery. Summary of the Invention

[0005] To address the above problems, this invention provides a low-energy-consumption method for preparing graphene battery electrodes using coal tar, achieving the goal of significantly reducing graphene growth temperature and saving energy while realizing the integrated preparation of high-performance self-supporting battery electrode materials and effectively controlling production costs.

[0006] This preparation method uses coal tar as a carbon source to grow graphene in situ on the surface of a foamed metal at a reaction temperature of 300℃-900℃, obtaining a graphene-metal composite substrate for synthesizing self-supporting electrode materials. By utilizing the characteristic that the molecular structure of coal tar is easily graphitized at lower temperatures and selecting foamed metal as a three-dimensional substrate, the high temperature (approximately 1000℃) required for the preparation of graphene by traditional chemical vapor deposition is reduced, thereby reducing energy consumption. Constructing electrodes with the graphene-metal composite substrate as the core lays the foundation for preparing self-supporting electrodes that eliminate the need for traditional coating processes and binders and conductive agents. In addition, the graphene obtained by low-temperature growth of coal tar has a high defect density, which can increase the lithium storage capacity and interfacial bonding strength of the electrode material, enhancing the electrochemical performance of the electrode.

[0007] Optionally, the low-energy-consumption method for preparing graphene battery electrodes from coal tar also includes: Active substance precursor loading step: The graphene-metal composite substrate is subjected to a hydrothermal reaction to load a metal (hydroxy) oxide precursor on its surface; Heat treatment conversion step: The precursor is heat-treated and converted into a metal oxide under an inert atmosphere.

[0008] Through the above-mentioned integrated process, the active material and the conductive framework are combined in situ. The resulting three-dimensional hierarchical porous structure is conducive to electrolyte wetting and rapid ion / electron transport, giving the electrode material high specific capacity and low charge transfer impedance.

[0009] Optionally, the low-energy-consumption method for preparing graphene battery electrodes from coal tar also includes: Coal tar separation steps: coal tar is obtained by graded pyrolysis of raw coal; The coal tar separation process includes the following steps: Crushing and drying steps: Crush the raw coal into particles with a diameter of less than 6mm and reduce the moisture content; Staged pyrolysis step: The dried coal particles are pyrolyzed in stages.

[0010] Coal tar separation further integrates the supply chain from raw materials to finished products, thereby further reducing raw material costs.

[0011] Optionally, pyrolysis gas is also generated in the staged pyrolysis step. In the low-temperature graphene growth step using coal tar, the pyrolysis gas is also introduced into the reactor for graphene growth as a carrier gas or reaction gas. The utilization of pyrolysis gas realizes the resource utilization of by-products, reduces dependence on external gas sources, and conforms to the principles of green manufacturing.

[0012] Optionally, the reaction temperature for the low-temperature graphene growth step using coal tar is 400℃-600℃. This preferred temperature range of 400℃-600℃ allows for efficient graphene growth while achieving a balance between energy consumption and material quality.

[0013] Optionally, in the heat treatment conversion step, the heat treatment temperature is 200℃-400℃, and the time is 1.5h-2.5h. The preferred heat treatment conversion conditions ensure complete conversion of the metal hydroxide to the metal oxide and form a stable interfacial bond, while avoiding potential damage to the graphene structure caused by excessively high temperatures.

[0014] Optionally, hydrogen peroxide solution is used as the oxidant in the hydrothermal reaction, the temperature of the hydrothermal reaction is 140℃-160℃, and the reaction time is 6h-24h. The preferred hydrothermal reaction conditions help to uniformly and controllably grow nanostructured metal hydroxide precursors on the surface of the graphene framework.

[0015] Optionally, coal tar is gasified using hydrogen as a carrier gas and then introduced into the reactor. The coal tar contains monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs), with MAHs comprising 60%-80% by mass and PAHs comprising 5%-20% by mass. The hydrogen flow rate is 10 sccm-30 sccm. Specific carbon source composition and process parameters help to promote the graphitization process at low temperatures, obtaining graphene with a suitable defect density. These defects can serve as additional active sites to enhance lithium storage capacity.

[0016] Optionally, the graphene loading on the graphene-metal composite substrate is 2-4 mg·cm³. - ². The range of loading capacity enables the electrode to have the capacity to carry conductive networks and active materials.

[0017] Optionally, this application also provides a continuous production system that applies any of the above-mentioned low-energy-consumption methods for preparing graphene battery electrodes using coal tar. This system enables continuous, large-scale production from raw material processing to electrode forming, improving production efficiency and providing a feasible industrialization path for low-cost manufacturing of high-performance electrodes. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation process of battery electrode materials in some embodiments of this application.

[0019] Figure 2 The images show Raman spectra of in-situ grown graphene from metal foam in some embodiments of this application.

[0020] Figure 3 This is a scanning electron microscope (SEM) image of the positive electrode of the battery electrode in some embodiments of this application.

[0021] Figure 4 This is a schematic diagram of the structure of a continuous battery electrode production system in some embodiments of this application.

[0022] Figure 5 This is a cyclic voltammetry curve of the positive electrode of a lithium battery in the second embodiment of this application.

[0023] Figure 6 This is an AC impedance diagram of the positive electrode of a lithium battery in the second embodiment of this application. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0025] <First Implementation Method> This embodiment provides a low-energy-consumption method for preparing graphene battery electrodes using coal tar, such as... Figure 1 As shown, it includes a coal tar separation step S1, a coal tar low-temperature graphene growth step S2, an active material precursor loading step S3, and a heat treatment conversion step S4.

[0026] Coal tar, a byproduct of coal chemical industry, is rich in polycyclic aromatic hydrocarbons (PAHs). Its molecular structure facilitates graphitization at lower temperatures, making it a low-cost solid carbon source. Using coal tar as a carbon source can reduce the temperature of traditional CVD processes (from approximately 1000℃ to 300℃-900℃). Coal tar sources include tar from coal tar separation or industrial byproducts, with a monocyclic aromatic hydrocarbon (PAH) mass fraction of 60%-80% and PAHs of 5%-20%. Coal tar rich in PAHs is easily graphitized at low temperatures, reducing energy consumption. The hydrogen flow rate can be controlled at 10-30 sccm as the carrier gas. The graphene loading is 2-4 mg·cm³. - ², to ensure the conductive network is fully functional.

[0027] Metal foam serves as both a three-dimensional substrate and a catalyst, and transition metal foams such as nickel foam or copper foam can be selected. Before use, the rolled metal foam undergoes a continuous cleaning line (including acid washing, alkali washing, deionized water rinsing, and drying) to ensure a clean surface.

[0028] In this embodiment, the coal tar separation step S1 includes a crushing and drying step S11 and a staged pyrolysis step S12, so that the low-rank raw coal is converted into coal tar for graphene growth with maximum efficiency.

[0029] Specifically, the coal tar separation step S1 in this embodiment includes the following steps: Crushing and drying step S11: The low-rank raw coal is crushed into particles with a diameter of less than 6mm by a crusher, and then the moisture content is reduced by the flue gas waste heat drying system (using the waste heat of subsequent processes) to improve the pyrolysis efficiency.

[0030] Staged pyrolysis step S12: The dried coal particles are conveyed into a moving bed or low-temperature carbonization furnace for staged pyrolysis. The reaction temperature is precisely controlled at 600℃ (this temperature range produces high-yield and suitable-quality tar). During this process, the coal undergoes thermal decomposition, producing three primary products: solid semi-coke, liquid crude coal tar, and gaseous pyrolysis gas. The semi-coke can be used for blast furnace injection, gasification, or sold as a clean solid fuel; the crude coal tar is rich in polycyclic aromatic hydrocarbons, which is the carbon source used in this embodiment to prepare graphene; the pyrolysis gas mainly contains H2, CH4, CO, etc., and has a high calorific value.

[0031] The continuous synthesis steps of the graphene battery electrode material in this embodiment include the following steps: Step S2: Low-temperature graphene growth from coal tar Substrate preparation step S21: Use foam metal with a pore size of 80-120 PPI, a surface density of 280-450 g·m-², and a thickness of 0.5-2 mm. Before use, pass the rolled foam metal through a continuous cleaning line (including pickling, alkali washing, deionized water rinsing and drying) to make the surface clean. Continuous Chemical Vapor Deposition (CVD) Step S22: A rolled, clean foamed metal strip is continuously passed through a CVD apparatus (e.g., a multi-zone tubular CVD furnace), allowing the foamed metal strip, coal tar, and pyrolysis gas to enter the reaction zone of the CVD apparatus together. Under an inert or reducing atmosphere (e.g., hydrogen), the reaction temperature is controlled at 300℃-900℃, preferably 400℃-600℃, for a reaction time of 1-5 minutes. The coal tar can be vaporized by heating to 100-300℃ and then introduced into the reaction zone, or it can be directly coated onto the foamed metal surface. During coal tar vaporization, hydrogen can be introduced as a carrier gas at a flow rate of 10-30 sccm to promote carbon source transport and reaction uniformity. The reaction pressure can be vacuum (50-500 Pa) or atmospheric pressure.

[0032] Cooling step S23: Subsequently, the above material enters the cooling zone and is cooled to room temperature at a rate of not less than 100℃ / min under a protective atmosphere to obtain a continuous graphene-metal composite substrate roll. The Raman spectrum of graphene on the foamed metal surface is as follows... Figure 2 As shown, peak D (1580 cm⁻¹) - ¹) This is obvious, indicating the presence of defects; 2D peak (2800 cm⁻¹) - ¹) The presence of graphene confirms the good quality of its honeycomb structure. The graphene loading was determined to be 2.8 mg·cm³ by gravimetric analysis. -2 Graphene exhibits a high defect density, with an Id / IG ratio greater than 0.8. These defects can serve as additional active sites, enhancing the lithium storage capacity and interfacial bonding strength of electrode materials, transforming the "defects" in traditional processes into performance advantages. This step significantly reduces energy consumption by lowering the temperature of traditional CVD processes (from approximately 1000℃ to 300℃-900℃), while simultaneously leveraging the low-cost characteristics of coal tar to achieve high-value utilization of carbon sources.

[0033] The active material precursor loading step S3 includes a surface activation treatment step S31 and a hydrothermal deposition step S32.

[0034] Surface activation treatment step S31: Immerse the graphene-metal composite substrate roll obtained in step S2 of low-temperature graphene growth from coal tar into a dilute hydrochloric acid solution with a volume ratio of 1:10, treat at room temperature for 30 minutes, remove and rinse with deionized water and dry.

[0035] Hydrothermal deposition step S32: The treated graphene-metal composite substrate is placed in a series of high-pressure continuous belt hydrothermal reactors or multiple high-pressure vessels (e.g., polytetrafluoroethylene high-pressure reactors), and continuously passed through a closed reaction chamber containing a hydrogen peroxide reaction solution. The volume fraction of the hydrogen peroxide solution is 1%-12%, preferably 5%-15%. The hydrothermal reaction is carried out at 120℃-180℃, preferably 140℃-160℃, for 6h-24h. The oxidant for the hydrothermal reaction is not limited to hydrogen peroxide; other mild oxidants (such as ozone aqueous solution) can also be used in similar reactions. After the reaction, metal hydroxide nanosheets or nanowire arrays grow on the surface of the composite substrate, forming a precursor composite material. This step achieves uniform deposition of the active material precursor under low-temperature conditions, avoiding high-temperature treatment, further reducing energy consumption, and laying the foundation for subsequent continuous thermal treatment.

[0036] The heat treatment conversion step S4 includes a drying step S41 and a continuous heat treatment step S42.

[0037] Drying process step S41: The wet strip of the load precursor is first passed through a drying channel to remove surface moisture.

[0038] Continuous heat treatment step S42: The dried strip of the loaded precursor is placed in a continuous programmable heat treatment device (e.g., a tunnel kiln) in an inert atmosphere (e.g., nitrogen) or air, and heated to 200℃-400℃, preferably 320℃-380℃, at a programmed heating rate of 1-10℃ / min, preferably 1-5℃ / min, for a reaction time of 1h-3h, preferably 1.5h-2.5h, followed by a holding time of 3-6h, to completely decompose the precursor into metal oxide. Finally, a rolled metal oxide / graphene / metal ternary self-supporting composite electrode material is obtained. The microstructure of the obtained composite electrode is as follows: Figure 3 As shown, a unique three-dimensional network / lace-like structure is presented, with the graphene framework serving as a conductive network to support the uniform distribution of metal oxide nanoparticles (size 8-15 nm). This step achieves phase transformation and interface strengthening of the active material through medium-temperature heat treatment, forming a three-dimensional hierarchical porous structure, which is beneficial for electrolyte wetting and ion / electron transport.

[0039] Furthermore, this embodiment employs a continuous production system to apply the above-described preparation method, achieving continuous roll-to-roll production. (See reference) Figure 4The continuous production system comprises a raw material processing unit, a continuous CVD unit, a continuous hydrothermal unit, and a continuous heat treatment unit connected in sequence. The raw material processing unit is used for coal tar separation; the continuous CVD unit is used for the reactive growth of graphene from coal tar; the continuous hydrothermal unit is used for precursor preparation; and the continuous heat treatment unit is used for the synthesis of self-supporting electrode materials. The continuous production system also integrates an electrode post-processing unit, which slices and stamps the electrode materials according to battery size requirements, integrating low-temperature graphene growth with electrode forming. Continuous operation reduces energy loss from intermittent production, further improving energy efficiency.

[0040] This embodiment uses coal tar as a low-cost carbon source to grow graphene in situ on the surface of foamed metal at a low temperature of 300℃-900℃. It integrates coal tar separation, active material precursor loading, and thermal treatment conversion steps, achieving reduced energy consumption (from the traditional 1000℃ to 300℃-900℃), reduced raw material costs (utilizing coal tar by-products and pyrolysis gas recycling), and simplified electrode preparation process (omitting the coating process and eliminating the need for binders and conductive agents). The prepared self-supporting electrode balances high active material loading and high interfacial bonding strength.

[0041] <Second Implementation Method> This embodiment provides an application example of the battery electrode material prepared according to the first embodiment. The metal oxide / graphene / metal ternary self-supporting composite electrode prepared by the method of the first embodiment is used to assemble batteries, such as lithium-ion batteries. Figure 5 and Figure 6 As shown, electrochemical performance tests revealed that its first-cycle discharge specific capacity reached 736 mAh / g, exhibiting good cycle stability; the AC impedance analysis of the lithium battery cathode showed that the battery charge transfer impedance was 102Ω, demonstrating excellent lithium storage performance and reaction kinetics.

[0042] The above are merely optional embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the low energy production of graphene battery electrodes from coal tar, characterized by, The method comprises the following steps: The coal tar low-temperature graphene growth step is to grow graphene on the surface of a foam metal in situ using coal tar as a carbon source, to obtain a graphene-metal composite substrate for synthesizing a self-supporting electrode material; The reaction temperature of the coal tar low-temperature graphene growth step is 300-900℃.

2. The method of claim 1, wherein the coal tar low energy graphene battery electrode is prepared by the steps of: The method further comprises the following steps: The active substance precursor loading step is to perform a hydrothermal reaction on the graphene-metal composite substrate to obtain a precursor loaded with metal (hydroxyl) oxide on the surface; The heat treatment conversion step is to heat and hold the precursor in an inert atmosphere, so that the precursor is converted into metal oxide.

3. The method of claim 1, wherein the coal tar low energy graphene battery electrode is prepared by, The method further comprises the following steps: The coal tar separation step is to perform fractional pyrolysis on raw coal to obtain coal tar; The coal tar separation step comprises the following steps: The crushing and drying step is to crush raw coal into particles with a particle size of less than 6 mm and reduce the moisture content; The fractional pyrolysis step is to perform fractional pyrolysis on the dried coal particles.

4. The method of claim 3, wherein the coal tar low energy graphene battery electrode is prepared by, In the fractional pyrolysis step, pyrolysis gas is also generated, and in the coal tar low-temperature graphene growth step, the pyrolysis gas is also introduced into the graphene growth reactor as carrier gas or reaction gas.

5. The method of claim 1, wherein the coal tar low energy graphene battery electrode is prepared by, The reaction temperature of the coal tar low-temperature graphene growth step is 400-600℃.

6. The method of claim 2, wherein the coal tar low energy graphene battery electrode is prepared by, In the heat treatment conversion step, the heat treatment temperature is 200-400℃, and the time is 1.5-2.5 h.

7. The method of claim 2, wherein the coal tar low energy graphene battery electrode is prepared by, The hydrothermal reaction uses hydrogen peroxide solution as an oxidant, the temperature of the hydrothermal reaction is 140-160℃, and the reaction time is 6-24 h.

8. The method of claim 1, wherein the coal tar low energy graphene battery electrode is characterized by, The coal tar is gasified using hydrogen as carrier gas and then introduced into the graphene growth reactor, the coal tar contains monocyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons, the mass fraction of monocyclic aromatic hydrocarbons is 60-80%, the mass fraction of polycyclic aromatic hydrocarbons is 5-20%, and the flow rate of the hydrogen is 10-30 sccm.

9. The method of claim 1, wherein the coal tar low energy graphene battery electrode is prepared by, The loading of graphene on the graphene-metal composite substrate is 2-4 mg-cm -2 .

10. A continuous production system, characterized by The method for preparing a graphene battery electrode with low energy consumption using coal tar is applied to the coal tar low-temperature graphene growth step in any one of claims 1-9.

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