Carbon material, method for preparing the same, and use thereof

Abstract

The application relates to the technical field of lithium ion battery materials, and discloses a carbon material and a preparation method and application thereof, the preparation method of the carbon material comprises the following steps: S1, dipping biomass material in an aqueous solution containing an activating agent to obtain post-dipping biomass material; the activating agent comprises a transition metal salt and a potassium salt; S2, freeze-drying the post-dipping biomass material to obtain a carbon material precursor; and S3, calcining the carbon material precursor to obtain the carbon material. The preparation method of the carbon material is mild in preparation condition, environmentally friendly, low in cost, and provides a new approach for the large-scale production of high-performance biomass carbon materials.

Description

Technical Field

[0001] This invention relates to the field of battery electrode materials technology, specifically to a carbon material, its preparation method, and its application. Background Technology

[0002] Supercapacitors, as a novel energy storage device, have broad application prospects in new energy vehicles, smart grids, and portable electronic products due to their advantages such as high power density, long cycle life, and fast charge / discharge speed. Electrode materials are the core determinant of supercapacitor performance; ideal capacitor electrode materials should possess high specific surface area, suitable pore structure to facilitate electrolyte ion migration, and good electronic conductivity.

[0003] Porous carbon materials have attracted much research attention as electrode materials for supercapacitors due to their high specific surface area, excellent electrical conductivity, and outstanding chemical and thermal stability. Activated carbon is currently the most commercially available electrode material, but its specific capacity is limited, and it is mainly derived from non-renewable fossil fuels, resulting in high cost and environmental unfriendliness. Biomass (such as wood, rice husks, and coconut shells) has become an ideal precursor for the preparation of porous carbon materials due to its wide availability, renewability, and low cost. However, carbon materials obtained by directly carbonizing biomass often have low specific surface area, incomplete pore structure development, and poor electrical conductivity, leading to poor electrochemical performance.

[0004] In the preparation of biomass-based carbon materials, chemical activation methods (such as using KOH) are often used to increase the specific surface area of ​​the carbon materials. However, these methods easily destroy the original excellent microstructure of biomass, and the pore structure of the prepared carbon materials is simple, mainly consisting of micropores. Although the specific surface area is high, it is not conducive to the rapid diffusion of large-sized ions, resulting in severe capacity decay and poor cycling performance at high current densities. Summary of the Invention

[0005] This invention provides a carbon material, its preparation method, and its application, in order to solve the problems in the prior art where the preparation process of biomass-based carbon materials easily damages the original microstructure, and the resulting carbon materials have a simple pore structure and poor cycle performance.

[0006] In a first aspect, the present invention provides a method for preparing a carbon material, comprising the following steps: Step S1: The biomass material is impregnated in an aqueous solution containing an activator to obtain impregnated biomass material; the activator includes transition metal salts and potassium salts; Step S2: Freeze-dry the impregnated biomass material to obtain a carbon material precursor; Step S3: Calcine the carbon material precursor to obtain the carbon material.

[0007] In one optional implementation, in step S1, the biomass material includes at least one of cotton, defatted cotton, hemp, and bamboo fiber.

[0008] In one alternative embodiment, the transition metal salt includes at least one of iron salt, cobalt salt, and nickel salt.

[0009] In one alternative embodiment, the potassium salt includes at least one of potassium citrate, potassium tartrate, and potassium dihydrogen phosphate.

[0010] In one alternative embodiment, the iron salt includes at least one of ferric chloride, ferric sulfate, and ferric nitrate.

[0011] In one alternative embodiment, the cobalt salt includes at least one of cobalt nitrate, cobalt chloride, and cobalt sulfate.

[0012] In one alternative embodiment, the nickel salt includes at least one of nickel chloride, nickel sulfate, and nickel nitrate.

[0013] In an optional embodiment, in step S1, the concentration of the transition metal salt in the aqueous solution containing the activator is 0.05-0.5M.

[0014] In one alternative embodiment, the concentration of the potassium salt in the aqueous solution containing the activator is 0.5-2M.

[0015] In one alternative embodiment, the molar ratio of the transition metal salt to the potassium salt is 1:3-10.

[0016] In one optional embodiment, the mass ratio of the biomass material to the volume of the activator aqueous solution is 1:50-100, wherein the mass-to-volume ratio is g / mL.

[0017] In one optional embodiment, the impregnation temperature is 20-60°C and the time is 6-24 hours.

[0018] In one optional embodiment, in step S2, the freeze-drying temperature is -50~-30℃, the vacuum degree is ≤10Pa, and the time is 12-36h.

[0019] In one alternative embodiment, a pre-freezing step is further included before freeze-drying.

[0020] In one alternative embodiment, the pre-freezing operation involves pre-freezing the impregnated biomass material in liquid nitrogen for 5-10 minutes.

[0021] In an optional embodiment, in step S3, the calcination operation involves heating the carbon material precursor from room temperature to 700-900°C at a heating rate of 1-5°C / min in a nitrogen and / or inert gas atmosphere and holding it at that temperature for 1-3 hours.

[0022] In one optional embodiment, the calcination process further includes steps of cooling, washing, and drying.

[0023] In one alternative implementation, the washing process includes acid washing and water washing.

[0024] In one optional embodiment, the concentration of the acid solution used for pickling is 0.8-1.2M.

[0025] In one optional embodiment, the acid solution used for pickling is selected from at least one of hydrochloric acid, sulfuric acid, and acetic acid.

[0026] In one alternative implementation, the pickling time is 4-8 hours.

[0027] In one optional embodiment, the drying temperature is 100-120°C and the time is 6-12 hours.

[0028] In one optional embodiment, step S1 is further divided into steps of washing and drying the biomass material.

[0029] In one optional embodiment, the cleaning operation involves ultrasonically cleaning the biomass material alternately with water and organic solvent 1-3 times.

[0030] In one optional embodiment, the drying temperature is 60-100°C and the time is 6-10 hours.

[0031] In one alternative embodiment, the frequency of the ultrasound is 20-40 kHz and the duration is 20-40 min.

[0032] In one alternative embodiment, the organic solvent includes ethanol and / or acetone.

[0033] In one optional embodiment, the mass ratio of the biomass material to the volume of water is 1:50-100, in g:mL.

[0034] In one optional embodiment, the mass ratio of the biomass material to the volume of the organic solvent is 1:10-100, in g:mL.

[0035] Secondly, the present invention provides carbon materials prepared by the above-mentioned method for preparing carbon materials.

[0036] In one optional embodiment, the specific surface area of ​​the carbon material is 2450-3000 m². 2 / g, total pore volume is 1.3-1.7cm³ 3 / g, of which mesopores account for 45-65%, micropores for 5-20%, and macropores for 15-40%. The International Union of Pure and Applied Chemistry (IUPAC) classifies pores in powder materials according to size into micropores (pore size <2nm), mesopores (pore size 2-50nm), and macropores (pore size >50nm).

[0037] Thirdly, the present invention provides the application of the above-mentioned carbon materials in the preparation of supercapacitors.

[0038] The technical solution of this invention has the following advantages: This invention provides a method for preparing carbon materials. By introducing a combination of transition metal salts and potassium salts as activators, catalytic etching of the carbon skeleton is achieved during the carbonization process. This successfully produces carbon materials with a predominantly mesoporous hierarchical pore structure without the use of highly corrosive activators (such as KOH). This pore structure is more conducive to the rapid diffusion of electrolyte ions, significantly improving the material's cycle performance. Furthermore, this invention employs a milder activator combined with freeze-drying technology, effectively avoiding the collapse and adhesion of the fibrous structure caused by high-temperature drying of biomass materials, thus preserving the fibrous microstructure of the biomass material in the prepared carbon material. The carbon material prepared by this invention can be directly used as a self-supporting electrode without the need for additional conductive agents and binders, which helps improve the electrochemical performance of the battery. Simultaneously, the predominantly mesoporous pore structure of the prepared carbon material results in a high specific surface area, facilitating the rapid diffusion of large-sized ions, exhibiting high specific capacity and excellent rate performance, making it better suited for application in the fabrication of supercapacitors. Furthermore, the preparation method of this invention is mild, environmentally friendly, and low-cost, providing a new approach for the large-scale production of high-performance biomass carbon materials. This invention also avoids the severe corrosion caused to equipment by using strong alkalis or acids as activators in existing technologies, and does not generate large amounts of wastewater in the post-treatment process, making it environmentally friendly. Attached Figure Description

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1This is a charge-discharge curve of the carbon materials prepared in Example 1 and Comparative Example 1 of the present invention at a current density of 0.5 A / g. Figure 2 This is a graph showing the cycle stability test results of the carbon material prepared in Example 1 of the present invention. Each point corresponds to 100 cycles, and a total of 3000 cycles are recorded. Detailed Implementation

[0041] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0042] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0043] Example 1 This embodiment provides a method for preparing carbon materials, including the following steps: (1) Take 3g of medical absorbent cotton and place it in 100mL of deionized water and 100mL of anhydrous ethanol respectively. Clean it by ultrasonic cleaning at a frequency of 30kHz for 30min. Repeat the ultrasonic cleaning operation twice. Then dry it in an oven at 80℃ for 8h to obtain dry absorbent cotton. (2) Prepare 200 mL of a mixed aqueous solution containing 0.1 M FeCl3 and 1.0 M potassium citrate. Immerse the dried defatted cotton completely in the mixed aqueous solution and soak it in a constant temperature water bath at 40 °C for 12 h to obtain the defatted cotton after soaking. (3) Take out the soaked and degreased cotton, pre-freeze it in liquid nitrogen for 5 min, and then transfer it to a freeze dryer and dry it at -45℃ and vacuum degree 5 Pa for 24 h to obtain carbon material precursor; (4) The carbon material precursor is placed in a tube furnace and heated from room temperature to 800°C at a rate of 2°C / min under an argon atmosphere, and held for 2 hours, and then cooled naturally. The black fibrous product obtained is soaked and stirred in 1M HCl solution for 6 hours, filtered, and the filtered solid product is washed with a large amount of deionized water until the washing solution is neutral. The solid is dried at 110°C for 10 hours to obtain the final carbon material.

[0044] pass Figure 1 It can be seen that the carbon material prepared in this embodiment successfully maintained the macroscopic fiber morphology of cotton fibers, and the surface was relatively rough, forming a large number of grooves and pores.

[0045] Example 2 This embodiment provides a method for preparing carbon materials, including the following steps: (1) Take 3g of medical absorbent cotton and place it in 50mL of deionized water and 10mL of anhydrous ethanol respectively. Clean it with ultrasonic at a frequency of 40kHz for 40min. Repeat the ultrasonic cleaning operation once. Then dry it in an oven at 60℃ for 10h to obtain dried absorbent cotton. (2) Prepare 150 mL of a mixed aqueous solution containing 0.5 M FeCl3 and 1.5 M potassium citrate. Immerse the dried defatted cotton completely in the mixed aqueous solution and soak it in a constant temperature water bath at 60 °C for 6 h to obtain the defatted cotton after soaking. (3) Take out the soaked and degreased cotton, pre-freeze it in liquid nitrogen for 10 min, and then transfer it to a freeze dryer and dry it for 36 h at -30℃ and vacuum degree 8 Pa to obtain carbon material precursor; (4) The carbon material precursor is placed in a tube furnace and heated from room temperature to 850°C at a rate of 5°C / min under a nitrogen atmosphere and held for 1 hour, and then cooled naturally. The black fibrous product obtained is soaked and stirred in 0.8M HCl solution for 8 hours, filtered, and the filtered solid product is washed with a large amount of deionized water until the filtrate is neutral. The filtered solid is dried at 100°C for 12 hours to obtain the final carbon material.

[0046] Example 3 This embodiment provides a method for preparing carbon materials, including the following steps: (1) Take 3g of medical absorbent cotton and place it in 75mL of deionized water and 50mL of anhydrous ethanol respectively. Clean it with ultrasonic waves at a frequency of 20kHz for 20min. Repeat the ultrasonic cleaning operation three times. Then dry it in an oven at 100℃ for 6h to obtain dry absorbent cotton. (2) Prepare 300 mL of a mixed aqueous solution containing 0.3 M Co(NO3)2 and 2 M potassium dihydrogen phosphate. Immerse the dried defatted cotton completely in the mixed aqueous solution and soak it in a constant temperature water bath at 20 °C for 24 h to obtain the defatted cotton after soaking. (3) Take out the soaked degreased cotton, pre-freeze it in liquid nitrogen for 8 min, and then transfer it to a freeze dryer and dry it for 12 h at -50℃ and 10 Pa vacuum to obtain carbon material precursor; (4) The carbon material precursor is placed in a tube furnace and heated from room temperature to 700°C at a rate of 1°C / min under an argon atmosphere, and held for 3 hours, and then cooled naturally. The resulting black fibrous product is soaked and stirred in 1.2M HCl solution for 4 hours, filtered, and the filtered solid product is washed with a large amount of deionized water until the filtrate is neutral. The filtered solid is dried at 120°C for 6 hours to obtain the final carbon material.

[0047] Comparative Example 1 This comparative example provides a method for preparing carbon materials, which is basically the same as that in Example 1, except that step (2) is omitted and the dried degreased cotton obtained in step (1) is used directly for step (3).

[0048] Comparative Example 2 This comparative example provides a method for preparing carbon materials, which is basically the same as that in Example 1, except that the mixed aqueous solution in step (2) contains only 0.1 M FeCl3.

[0049] Comparative Example 3 This comparative example provides a method for preparing carbon materials, which is basically the same as that in Example 1, except that the mixed aqueous solution in step (2) contains only 1.0 M potassium citrate.

[0050] Comparative Example 4 This comparative example provides a method for preparing carbon materials, which is basically the same as that in Example 1, except that step (3) is replaced by: taking out the soaked and degreased cotton and drying it in an oven at 40°C for 12 hours to obtain the carbon material precursor; other steps remain unchanged.

[0051] Experimental Example 1 This experimental example tests the structure of the carbon materials prepared in each embodiment and comparative example.

[0052] 1. Testing Method Referring to GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Materials by Gas Adsorption BET Method" and GB / T 21650.2-2008 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Method - Part 2: Analysis of Mesopores and Macropores by Gas Adsorption Method", low-temperature nitrogen isothermal adsorption-desorption analysis was performed on carbon materials prepared in various examples and comparative examples under liquid nitrogen bath conditions using a fully automated BET specific surface area analyzer. The specific surface area, pore size, and pore volume of the samples were equivalently calculated using Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), and density functional theory (DFT) methods.

[0053] 2. Test Results Table 1. Test results of carbon material structure

[0054] As shown in Table 1, Examples 1-3 introduced a combination of transition metal salts and potassium salts as activators in the preparation of carbon materials, resulting in carbon materials with a predominantly mesoporous structure and a larger specific surface area. This structure is more conducive to the rapid diffusion of electrolyte ions. In contrast, Comparative Examples 1-3 obtained carbon materials with a smaller specific surface area and a predominantly microporous structure by not using an activator or by using only one activator, which is not conducive to the rapid diffusion of large-sized ions. Comparative Example 4 used high-temperature drying, which caused changes in the fiber structure of the biomass material, resulting in a smaller specific surface area and a higher proportion of micropores and macropores.

[0055] Experimental Example 2 This experimental example tests the electrochemical performance of the carbon materials prepared in each embodiment and comparative example.

[0056] 1. Testing Method The charge storage behavior of the prepared materials was tested using a three-electrode system, with Ag / AgCl and platinum electrodes used as the reference and auxiliary electrodes, respectively, and a 6M KOH aqueous solution as the electrolyte. The prepared carbon material, conductive graphite, and polytetrafluoroethylene (PTFE) were uniformly mixed in a mass ratio of 80:15:5 to form a slurry, which was then coated onto 1.0 × 1.0 cm nickel foam and dried in a 60℃ oven for 12 h. Electrode sheets were then fabricated under a pressure of 10 MPa using a tablet press, with each electrode sheet containing 2.0 mg of carbon material. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests were performed on a CHI 660E electrochemical workstation from Shanghai Chenhua Co., Ltd.

[0057] Measurements were taken within a voltage range of 0-1V. The specific capacitance was obtained by cycling at 0.5A / g for 10 cycles, then at 2A / g for 10 cycles, and finally at 2A / g for 3000 cycles. The specific capacitance was calculated based on the GCD discharge curve as follows:

[0058] Where Cm is the specific capacitance in F / g, I (mA) is the discharge current, Δt (s) is the discharge time, ΔV (V) is the potential range difference, and m (mg) is the mass of carbon material coated on a single electrode. Capacitance retention rate after 3000 cycles at a current density of 2A / g = (Specific capacitance after 3000 cycles at a current density of 2A / g) / (Specific capacitance after 10 cycles at a current density of 2A / g) × 100%.

[0059] 2. Test Results Table 2 Electrochemical performance test results

[0060] From Table 2, Figure 2 It can be seen that the carbon materials obtained in Examples 1-3 exhibit excellent electrochemical performance at a current density of 0.5 A / g, and the cyclic voltammetry curves of Example 1 maintain an approximately rectangular shape at different scan rates, without obvious redox peaks, indicating that it has good double-layer capacitance characteristics and rapid ion response. The specific capacitance and cycling performance of the carbon materials obtained in Comparative Examples 1-4 are not as good as those in Examples 1-3.

[0061] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a carbon material, characterized in that, Includes the following steps: Step S1: The biomass material is impregnated in an aqueous solution containing an activator to obtain impregnated biomass material; the activator includes transition metal salts and potassium salts; Step S2: Freeze-dry the impregnated biomass material to obtain a carbon material precursor; Step S3: Calcine the carbon material precursor to obtain the carbon material.

2. The method for preparing carbon materials according to claim 1, characterized in that, In step S1, the biomass material includes at least one of cotton, defatted cotton, hemp, and bamboo fiber; And / or, the transition metal salt includes at least one of iron salt, cobalt salt, and nickel salt; And / or, the potassium salt includes at least one of potassium citrate, potassium tartrate, and potassium dihydrogen phosphate; Optionally, the iron salt includes at least one of ferric chloride, ferric sulfate, and ferric nitrate; Optionally, the cobalt salt includes at least one of cobalt nitrate, cobalt chloride, and cobalt sulfate; Optionally, the nickel salt includes at least one of nickel chloride, nickel sulfate, and nickel nitrate.

3. The method for preparing carbon materials according to claim 1, characterized in that, In step S1, the concentration of the transition metal salt in the aqueous solution containing the activator is 0.05-0.5M; And / or, the concentration of the potassium salt in the aqueous solution containing the activator is 0.5-2M; And / or, the molar ratio of the transition metal salt to the potassium salt is 1:3-10; And / or, the mass ratio of the biomass material to the volume of the activator aqueous solution is 1:50-100, wherein the mass-to-volume ratio is g / mL; And / or, the impregnation temperature is 20-60°C and the time is 6-24 hours.

4. The method for preparing carbon materials according to claim 1, characterized in that, In step S2, the freeze-drying temperature is -50~-30℃, the vacuum degree is ≤10Pa, and the time is 12-36h; And / or, the freeze-drying process further includes a pre-freezing step; Optionally, the pre-freezing operation involves pre-freezing the impregnated biomass material in liquid nitrogen for 5-10 minutes.

5. The method for preparing carbon materials according to claim 1, characterized in that, In step S3, the calcination operation involves heating the carbon material precursor from room temperature to 700-900℃ in a nitrogen and / or inert gas atmosphere at a heating rate of 1-5℃ / min and holding it at that temperature for 1-3 hours. And / or, the calcination process further includes steps of cooling, washing, and drying; Optionally, the washing includes pickling and water washing; more preferably, the concentration of the acid solution used for pickling is 0.8-1.2M; more preferably, the acid solution used for pickling is selected from at least one of hydrochloric acid, sulfuric acid, and acetic acid; more preferably, the pickling time is 4-8 hours. Optionally, the drying temperature is 100-120℃ and the time is 6-12h.

6. The method for preparing carbon materials according to any one of claims 1-5, characterized in that, The step S1 is preceded by a step of cleaning and drying the biomass material; Optionally, the cleaning operation involves alternating ultrasonic cleaning of the biomass material with water and organic solvent 1-3 times; Optionally, the drying temperature is 60-100℃ and the time is 6-10h.

7. The method for preparing carbon materials according to claim 6, characterized in that, The frequency of the ultrasound is 20-40kHz, and the duration is 20-40min; And / or, the organic solvent includes ethanol and / or acetone; And / or, the mass ratio of the biomass material to the volume of water is 1:50-100, in g:mL; And / or, the mass ratio of the biomass material to the volume of the organic solvent is 1:10-100, in g:mL.

8. The carbon material prepared by the method of any one of claims 1-7.

9. The carbon material according to claim 8, characterized in that, The specific surface area of ​​the carbon material is 2450-3000 m². 2 / g, total pore volume is 1.3-1.7cm³ 3 / g, of which the mesoporous pore volume accounts for 45-65%, the microporous pore volume accounts for 5-20%, and the macroporous pore volume accounts for 15-40%.

10. The application of the carbon material according to claim 9 in the preparation of supercapacitors.

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