A preparation method and application of porous carbon material with improved rate performance

Abstract

The present invention provides a method for preparing and applying a porous carbon material with improved rate performance, comprising the following steps: 1) dispersing alkali lignin in water, adding alkali solution dropwise, stirring until the alkali lignin is completely dissolved, adding formaldehyde solution dropwise for hydroxymethylation, adjusting the pH to near neutral, performing vacuum distillation, filtering, and adjusting the concentration with water to obtain hydroxymethylated alkali lignin, which is used as a carbon source for later use; 2) dissolving a template in a solvent to obtain a template solution; 3) uniformly mixing the carbon source, nitrogen source, phosphorus source, and template solution, controlling the temperature to volatilize the solvent, then heating and solidifying the mixture, and grinding the mixture into a powder to obtain a composite primary product; 4) low-temperature calcining and high-temperature carbonization of the polymer composite primary product under an inert atmosphere to obtain a porous carbon material; the nitrogen source is a phenyldiethanolamine derivative, and the phosphorus source is a tricarboxylic acid-based phosphorus compound. The porous carbon material has excellent rate performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon materials, and in particular relates to a preparation method and application of a porous carbon material with improved rate performance. Background Art

[0002] With the depletion of oil resources and the deteriorating environment, energy development and conservation have become a critical issue worldwide. Energy materials and energy storage devices, as key components, are closely linked to the economy, resources, and the environment, and have long been a research priority worldwide. As power density requirements for energy storage devices in many fields continue to rise, exceeding the capabilities of batteries, supercapacitors—new energy storage components with power and energy densities between those of traditional capacitors and secondary batteries—are rapidly developing.

[0003] Based on the electrode materials used, supercapacitors can be categorized as carbon electrode supercapacitors, precious metal oxide electrode supercapacitors, and conductive polymer electrode supercapacitors. Porous carbon material-based supercapacitors are carbon electrode supercapacitors. Because porous carbon has a good pore size distribution, large specific surface area, and good conductivity, electrolyte ions can migrate freely within the pores, quickly forming a double layer, reducing the capacitance dispersion effect, and possessing strong charge and discharge capabilities, making them ideal electrode materials for supercapacitors.

[0004] Lignin, a crucial component of plant cell walls, is widely found in plant materials such as wood, straw, fruit shells, and leaves. It is widely available and abundant. Using lignin as a carbon source in the preparation of porous carbon materials not only maximizes its value but also conserves energy and resources.

[0005] For example, the lignin-based hierarchical porous carbon material and its preparation method disclosed in patent CN109019590B include: lignin pretreatment, preparation of a low eutectic solvent, thermal carbonization of the low eutectic solvent of lignin, preparation of a solvent thermal carbonization product, activation of the solvent thermal carbonization product, and preparation of a lignin-based hierarchical porous carbon material.

[0006] Patent CN106744793B discloses an alkali lignin-based porous carbon material for supercapacitors, and its preparation method and application. Crudely purified alkali lignin from papermaking black liquor is mixed with a triblock polymer Pluronic F127 and Mg(CH3COO)2·4H2O, and formaldehyde and hydrochloric acid are added and stirred thoroughly to obtain a mixed solution; the mixed solution is placed in an oven to dry to obtain a dark brown solid; the dark brown solid is then placed in a tubular furnace for a carbonization reaction. After the reaction is completed, nitrogen or inert gas is continuously introduced to cool to room temperature; finally, the porous carbon material is acid-washed, washed with water, and dried to obtain a black powder.

[0007] The above porous carbon materials are prepared using lignin as raw material through catalytic activation method or soft template method, which have large specific surface area and rich pore structure. However, since the structure of lignin itself is relatively loose and irregular, it is mainly composed of phenylpropane units connected by ether bonds and carbon-carbon bonds. This structure is prone to collapse during the heat treatment and carbonization process, resulting in complex pore structure and defects, which is not conducive to the diffusion of electrolyte ions and poor rate performance of supercapacitors. Summary of the Invention

[0008] In order to solve the above technical problems, the present invention provides a method for preparing a porous carbon material with improved rate performance and its application. Hydroxymethylated alkali lignin is used as a carbon source, phenyldiethanolamine derivatives are used as a nitrogen source, and tricarboxylic acid-based phosphorus-containing compounds are used as a phosphorus source. By means of self-assembly, high-temperature carbonization and other processes, a phosphorus-nitrogen-doped porous carbon material with excellent rate performance is prepared.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A method for preparing a porous carbon material with improved rate performance comprises the following steps:

[0011] 1) dispersing alkali lignin into water, adding alkali solution dropwise, stirring until the alkali lignin is completely dissolved, adding formaldehyde solution dropwise for hydroxymethylation, adjusting the pH to be close to neutral, distilling under reduced pressure, filtering, and adjusting the concentration with water to obtain hydroxymethylated alkali lignin as a carbon source for later use;

[0012] 2) dissolving the template in a solvent to obtain a template solution;

[0013] 3) uniformly mixing the carbon source, nitrogen source, phosphorus source, and template solution, controlling the temperature to volatilize the solvent, then heating and solidifying, and grinding into powder to obtain a composite primary product;

[0014] 4) Under an inert atmosphere, the polymer composite primary product is subjected to low-temperature calcination and high-temperature carbonization to obtain a porous carbon material;

[0015] The nitrogen source is a phenyldiethanolamine derivative, and the phosphorus source is a tricarboxylic acid-based phosphorus-containing compound.

[0016] In step 1), the weight-average molecular weight of the alkali lignin is 1000-3000. The mass ratio of the alkali lignin to water is 1:4-6. Lignin is an aggregate with many polar groups in its structure, especially more hydroxyl groups, which form strong intramolecular and intermolecular hydrogen bonds. Therefore, lignin is insoluble in water and any solvent, but alkali lignin is degraded lignin and can be dissolved in dilute water, alkaline or neutral polar solvents. The alkali lignin is selected from at least one of wood pulp alkali lignin, bamboo pulp alkali lignin, wheat straw pulp alkali lignin, reed pulp alkali lignin, bagasse pulp alkali lignin, and asparagus pulp alkali lignin. The alkali solution is added dropwise to adjust the pH to 11-13; the alkali solution is a 30-40wt% sodium hydroxide solution or potassium hydroxide solution. The formaldehyde solution is a 30-40wt% formaldehyde aqueous solution. The mass ratio of the alkali lignin to the formaldehyde solution is 1:1.5-1.8. The formaldehyde solution is dripped over a period of 0.5-1.5 hours. The hydroxymethylation reaction is performed by heating the temperature to 65-80°C and reacting for 1-3 hours. The second pH adjustment is performed using a 5-10 wt% dilute hydrochloric acid solution. The vacuum distillation is performed at a negative pressure of -0.090 to -0.098 MPa and 35-55°C for 3-5 hours. The filtration is performed to remove salts. The concentration is adjusted to 20-30 wt%.

[0017] Step 2) The template is a nonionic surfactant, specifically selected from one or a combination of two or more of F127, P123, and Brij76. The solvent is selected from one or a combination of two of ethanol and isopropanol. The concentration of the template solution is 5-8 wt%.

[0018] In step 3), the phenyldiethanolamine derivative is selected from one or a combination of two or more of N-benzyldiethanolamine, N-phenyldiethanolamine, N,N-dihydroxyethyl-m-toluidine, and N,N-dihydroxyethyl-o-methylaniline; and the tricarboxylic acid-containing phosphorus compound is selected from one or a combination of two or more of 2-phosphonobutane-1,2,4-tricarboxylic acid, 2-(phosphinoyl)propane-1,2,3-tricarboxylic acid, and 3-phospho-1,3,5-pentanetricarboxylic acid.

[0019] The mass ratio of the carbon source, nitrogen source, phosphorus source and template solution is 3:0.5-1:0.8-1:10-12. The temperature control is to control the temperature at 20-40°C, and the temperature rise curing is to rise to 100-120°C for 12-36 hours.

[0020] The carboxyl groups on the phosphorus source react with the hydroxyl groups on the nitrogen source and the carbon source during the temperature-raising solidification process to form a cross-connected three-dimensional network structure, which can reduce the collapse during the heat treatment carbonization process.

[0021] In step 4), the low-temperature calcination is performed by heating the material to 300-500°C at a rate of 1-3°C and maintaining the temperature for 1-2 hours, and the high-temperature carbonization is performed by heating the material to 600-1000°C at a rate of 2-10°C and maintaining the temperature for 3-5 hours.

[0022] A porous carbon material with improved rate performance is prepared by the above method.

[0023] The present invention also provides an application of the porous carbon material for improving rate performance, wherein the porous carbon material is applied to a supercapacitor.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention uses hydroxymethylated alkali lignin as a carbon source, phenyldiethanolamine derivatives as a nitrogen source, and tricarboxylic acid-based phosphorus-containing compounds as a phosphorus source, and uses self-assembly, high-temperature carbonization and other processes to prepare a phosphorus-nitrogen doped porous carbon material with excellent rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the pore size distribution curve of the porous carbon material prepared in Example 1. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with specific embodiment, but is not limited to the content on the specification sheets. Unless otherwise specified, "parts" described in the embodiments of the present invention are all parts by weight. All reagents used are commercially available reagents in this area.

[0028] Wood pulp alkali lignin was purchased from Xinyi Feihuang Chemical Co., Ltd. with a weight-average molecular weight of 2500.

[0029] Example 1

[0030] 1) Dispersing 100 parts of wood pulp alkali lignin in 500 parts of water, adding 40 wt% sodium hydroxide to adjust the pH to 11.5, stirring at 250 r / min until the solution is completely dissolved, adding 180 parts of 37 wt% formaldehyde solution to carry out hydroxymethylation, and completing the addition for 1 hour. Adjusting the pH to neutral with 5 wt% dilute hydrochloric acid solution, distilling under reduced pressure at 35° C. and negative pressure of -0.098 MPa for 3 hours, filtering to remove the precipitated sodium chloride, adding water to adjust the concentration to 20 wt%, and obtaining hydroxymethylated alkali lignin as a carbon source for later use;

[0031] 2) dissolving 8 parts of the template agent F127 in 92 parts of ethanol to obtain a template agent F127 solution with a concentration of 8 wt%;

[0032] 3) 30 parts of a carbon source, 5 parts of a nitrogen source, N-benzyldiethanolamine, 10 parts of a phosphorus source, 2-phosphonobutane-1,2,4-tricarboxylic acid, and 10 parts of a template F127 solution were mixed evenly, the mixture was kept at 40°C for 48 hours to evaporate the water, then the mixture was heated to 100°C and cured for 16 hours, and finally ground into powder to obtain a composite primary product;

[0033] 4) Under a nitrogen atmosphere, the polymer composite primary product was added to a tubular furnace, heated to 400°C at a rate of 1°C / min, and calcined at 400°C for 1.5 hours, heated to 700°C at a rate of 1°C / min, and carbonized at 700°C for 4 hours to obtain a porous carbon material.

[0034] Example 2

[0035] The rest is the same as Example 1, except that in step 3), 2-(phosphinooxy)propane-1,2,3-tricarboxylic acid is used instead of 2-phosphonobutane-1,2,4-tricarboxylic acid with an equal mass.

[0036] Example 3

[0037] The rest is the same as Example 1, except that in step 3), the amount of 2-phosphonobutane-1,2,4-tricarboxylic acid used is 8 parts.

[0038] Example 4

[0039] The rest is the same as Example 1, except that, in step 3), the amount of 2-phosphonobutane-1,2,4-tricarboxylic acid used is 12 parts.

[0040] Example 5

[0041] The rest is the same as Example 1, except that, in step 3), the amount of 2-phosphonobutane-1,2,4-tricarboxylic acid used is 6 parts.

[0042] Example 6

[0043] The rest is the same as Example 1, except that, in step 3), 20 parts of a carbon source, 10 parts of a nitrogen source N-benzyldiethanolamine, 10 parts of a phosphorus source 2-phosphonobutane-1,2,4-tricarboxylic acid, and 12 parts of a template F127 solution are mixed evenly, the temperature is controlled at 40° C. for 48 hours to evaporate the water, and then the temperature is raised to 100° C. for curing for 16 hours, and finally ground into powder to obtain a composite primary product.

[0044] Comparative Example 1

[0045] The rest is the same as Example 1, except that N-ethyldiethanolamine of equal mass is used instead of N-benzyldiethanolamine.

[0046] Comparative Example 2

[0047] The rest is the same as Example 1, except that an equal mass of propanetricarboxylic acid is used instead of 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0048] Preparation of working electrode

[0049] Application Example 1

[0050] The porous carbon material, conductive graphite and polytetrafluoroethylene emulsion of Example 1 were mixed in a mass ratio of 8:1:1, an appropriate amount of anhydrous ethanol was added as a dispersant, and the mixture was uniformly mixed using an ultrasonic disperser for 30 minutes. The resulting slurry was placed in an 80°C blast drying oven and steamed until viscous. The slurry was evenly coated on a disc-shaped nickel foam with a brush and placed in a vacuum drying oven at 80°C for 12 hours. A fully dried electrode sheet was pressed using a manual powder tablet press at a pressure of 12 MPa for 60 seconds to obtain an active material mass of 3 mg / cm 2 working electrode.

[0051] Application Example 2

[0052] The rest is the same as Application Example 1, except that the porous carbon material is prepared according to Examples 2-6.

[0053] Comparative Application Examples 1-2

[0054] The rest is the same as Application Example 1, except that the porous carbon material is prepared according to Comparative Example 1-2.

[0055] The porous carbon materials prepared in the above examples and comparative examples were subjected to the following pore structure and specific surface area performance tests, and the working electrodes prepared in the application examples and comparative application examples were subjected to rate performance tests:

[0056] 1. Pore structure and specific surface area: measured by NOVA 1000e pore structure specific surface area tester. The sample was degassed at 350℃ for 2h and adsorbed with liquid nitrogen at 77K and relative pressure (P / P0) 10 -6 N2 adsorption was carried out in the range of -1, and the specific surface area was calculated by the BET equation.

[0057] 2. Rate performance: A metal Pt electrode was used as the counter electrode, a Hg / HgO electrode was used as the reference electrode, and the electrolyte was a 6 mol / L KOH solution. The working electrode was immersed in a 6 mol / L KOH solution for 24 hours before testing. A CHI660C electrochemical workstation from Shanghai Chenhua Instrument Co., Ltd. was used to perform constant current charge and discharge tests on the electrode at current densities of 0.5 A / g and 20 A / g. The specific capacitance retention at a current density of 20 A / g compared to 0.5 A / g was calculated.

[0058] The specific capacitance is calculated based on the charge and discharge test. The specific capacitance at different current densities is calculated using the following formula:

[0059] C=I*Δt / (m*ΔV)

[0060] Where I is the discharge current, A; Δt is the discharge time, s; m is the mass of the active material, g; ΔV is the actual discharge potential drop, V.

[0061] Table 1 Performance test results

[0062]

[0063] Depend on Figure 1 It can be seen that the porous carbon material prepared by the present invention has a bimodal pore structure, one of which is sharper and distributed in the micropore region and is concentrated at around 1.5-2 nm, and the other is distributed in the mesopore region and is concentrated at around 10-15 nm. This bimodal pore size distribution enables it to have both concentrated and rich mesopores and a large specific surface area. A large number of mesopores provide a good channel for the rapid migration of ions. It can be seen from Table 1 that the porous carbon material prepared by the present invention has a high specific surface area and an appropriate pore structure. When it is applied to a supercapacitor with a current density of 0.5 A / g, the specific capacitance of the preferred application example is as high as 397.6 A / g, and it has a good transport capacity for ions; when the current density increases to 20 A / g, the specific capacitance value retention rate is as high as 71.8%, which is smaller than the specific capacitance attenuation of comparative application example 1 and comparative application example 2, showing good rate performance, which is mainly attributed to its high mesoporosity and specific surface area.

[0064] Comparative Application Example 1, in which an equal amount of N-ethyldiethanolamine was substituted for N-benzyldiethanolamine, exhibited poor rate performance, presumably due to a weak pore structure and the resulting collapse of numerous micropores after heat treatment. Comparative Application Example 2, in which an equal amount of propanetricarboxylic acid was substituted for 2-phosphonobutane-1,2,4-tricarboxylic acid, also exhibited poor rate performance, presumably due to a smaller specific surface area, a less complex pore structure, and poor wettability to the electrolyte.

[0065] It can be clearly seen from the application examples and comparative application examples that the nitrogen source and phosphorus source of the present invention have a significant synergistic effect of improving the rate performance of alkali lignin.

[0066] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A method for preparing a porous carbon material with improved rate performance, characterized in that: The steps include: 1) Disperse alkali lignin in water, add alkali solution dropwise, stir until the alkali lignin is completely dissolved, add formaldehyde solution dropwise for hydroxymethylation, adjust the pH to neutral, distill under reduced pressure, filter, and adjust the concentration with water to obtain hydroxymethylated alkali lignin and use it as a carbon source for later use; 2) dissolving the template in a solvent to obtain a template solution; 3) Evenly mix the carbon source, nitrogen source, phosphorus source, and template solution, control the temperature to evaporate the solvent, then heat and solidify, grind into powder to obtain the composite primary product; 4) Under an inert atmosphere, the polymer composite primary product is subjected to low-temperature calcination and high-temperature carbonization to obtain a porous carbon material; The nitrogen source is a phenyldiethanolamine derivative, and the phosphorus source is a tricarboxylic acid-based phosphorus-containing compound; The phenyldiethanolamine derivative is selected from one or more of N-benzyldiethanolamine, N-phenyldiethanolamine, N,N-dihydroxyethyl-m-toluidine, and N,N-dihydroxyethyl-o-methylaniline; the tricarboxylic acid-containing phosphorus compound is selected from one or more of 2-phosphonobutane-1,2,4-tricarboxylic acid, 2-(phosphinoyl)propane-1,2,3-tricarboxylic acid, and 3-phospho-1,3,5-pentanetricarboxylic acid; The mass ratio of the carbon source, nitrogen source, phosphorus source and template solution is 3:0.5-1:0.8-1:10-12.

2. The method for preparing a porous carbon material with improved rate performance according to claim 1, characterized in that: Step 1) The alkali lignin has a weight average molecular weight of 1000-3000; when the alkali lignin is dispersed in water, the mass ratio of the alkali lignin to water is 1:4-6.

3. The method for preparing a porous carbon material with improved rate performance according to claim 1, characterized in that: Step 1) adding alkaline solution to adjust the pH to 11-13; the concentration is adjusted to 20-30 wt%.

4. The method for preparing a porous carbon material with improved rate performance according to claim 1, wherein: Step 1) The alkali lignin is selected from at least one of wood pulp alkali lignin, bamboo pulp alkali lignin, wheat straw pulp alkali lignin, reed pulp alkali lignin, bagasse pulp alkali lignin, and sedge pulp alkali lignin; Step 2) The template is a non-ionic surfactant, specifically selected from one or more of F127, P123, and Brij76; the solvent is selected from one or two of ethanol and isopropanol; and the concentration of the template solution is 5-8wt%.

5. The method for preparing a porous carbon material with improved rate performance according to claim 1, wherein: Step 3) The temperature control is to control the temperature at 20-40°C, the temperature rise and curing is to heat the temperature to 100-120°C for curing, and the curing time is 12-36 hours.

6. The method for preparing a porous carbon material with improved rate performance according to claim 1, wherein: Step 4) The low-temperature calcination is to increase the temperature to 300-500°C at a rate of 1-3°C and maintain it for 1-2 hours, and the high-temperature carbonization is to increase the temperature to 600-1000°C at a rate of 2-10°C and maintain it for 3-5 hours.

7. A porous carbon material with improved rate performance, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 6.

8. The use of the porous carbon material according to claim 7, characterized in that: Used in supercapacitors.

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