Porous carbon material with adjustable pore diameter as well as preparation method and application of porous carbon material

Abstract

The invention relates to an aperture-adjustable porous carbon material and a preparation method and application thereof. The preparation method comprises the following steps: adding an alkali solution into a phenol source, stirring, heating to 60-90 DEG C, adding an aldehyde source solution, stirring, cooling to room temperature, and adding an acid solution to adjust the mixed solution to be neutral, so as to obtain a phenolic resin oligomer solution; evaporating water, and adding low-carbon alcohol to prepare a phenolic aldehyde low-carbon alcohol solution; preparing silicon dioxide sol, wherein the particle size of silicon dioxide particles is controlled by adjusting the pH value; the preparation method comprises the following steps: mixing and stirring a phenolic low-carbon alcohol solution and silicon dioxide sol at 35-45 DEG C, washing, filtering and drying to obtain a silicon dioxide-phenolic resin composite carbon source; carrying out carbonization treatment on the silicon dioxide-phenolic resin composite carbon source to obtain a carbonized product with a carbon skeleton and an S O < 2 > template; and carrying out wet etching treatment on the carbonized product, selectively etching the S < O2 > template so as to form holes in positions occupied by S < O2 > particles, and then washing, filtering and drying to obtain the porous carbon material with the adjustable aperture.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of porous carbon material preparation, and particularly relates to a porous carbon material with adjustable pore size and a preparation method and application thereof. BACKGROUND

[0002] With the progress of science and technology and the development of industry, people's requirements for material performance are getting higher and higher. Among numerous new materials, porous carbon materials are attracting much attention due to their unique structure and excellent performance. Porous carbon material is a kind of carbon material with highly developed pore structure, and the pore size, distribution and morphology of the material have an important influence on the performance of the material. By adjusting the pore size, porous carbon materials with different pore structures can be prepared to meet the needs of different fields.

[0003] Microporous carbon material is a carbonaceous material with rich microporous structure, and the pore size is usually less than 2 nm. Due to its unique pore structure and excellent physical and chemical properties, this kind of material has shown wide application potential in gas adsorption and separation, energy storage, catalyst carrier, environmental protection, biomedicine and other fields. Microporous carbon material not only has high specific surface area, good electrical conductivity and thermal stability, but also shows excellent adsorption performance and catalytic activity. Mesoporous carbon material has a pore size of 2-50 nm, and common preparation is usually by template method, which is suitable for applications requiring large molecule or ion transmission, such as catalyst carrier, adsorption and release of biomolecules. Macroporous carbon material has a pore size of more than 50 nm, which is suitable for applications requiring fast mass transfer and low pressure drop, such as fluid filtration, electrode materials, etc. Different pore sizes correspond to different applications, so it is necessary to prepare porous carbon materials with different pore sizes. Common preparation methods include activation method, hard template method, etc. The hard template method usually uses nanosilica as a hard template, and the smaller the particle size, the more expensive the cost. In the dispersion process, silica is easy to aggregate, resulting in uneven pore size distribution, affecting the electrochemical performance of the material, and further affecting the overall performance of the battery.

[0004] Zhou et al. directly used nanosilica sol as a hard template and prepared mesoporous carbon spheres with adjustable pore size of 7-22 nm by spray drying method (Zhou, J. G. Preparation of mesoporous / hollow carbon microspheres by spray drying method and its application research[D]. East China University of Technology, 2016). However, nanosilica has strong van der Waals interaction, so the dispersion problem in the solvent is difficult to solve, which will lead to aggregation and result in larger and non-uniform pore size of the subsequent porous carbon material. Moreover, nanosilica sol has high cost and is not suitable for large-scale industrial production.

[0005] Therefore, developing a preparation method for obtaining a porous carbon material with a relatively concentrated pore size distribution can maximize the advantages of different pore sizes, meet different needs, and provide strong support for further optimizing the electrochemical performance of the porous carbon material, which is a key problem urgently to be solved in the current research field. SUMMARY

[0006] The present application aims to provide a porous carbon material with adjustable pore size and a preparation method and application thereof, so as to overcome the problems in the prior art, such as difficulty in dispersing templates, uneven pore size, complex preparation process, and limited electrochemical performance of carbon materials. By introducing a controllable particle size of silica sol as a hard template, and after compounding with a phenolic resin oligomer, carbonization and etching treatment, the controllable construction of a porous structure is realized, thereby preparing a porous carbon material with uniform pore size distribution, high specific surface area, and excellent cycle stability, which is particularly suitable for energy storage materials, lithium ion battery anodes, and other fields.

[0007] To achieve the above-mentioned purpose, in a first aspect, the present application provides a preparation method of a porous carbon material with adjustable pore size, comprising:

[0008] In a container at 25-50℃, a phenol source is added, then a first alkali solution is added and stirred, after that, the temperature is raised to 60-90℃, then an aldehyde source solution is added and stirred, and finally, the temperature is cooled to room temperature, a first acid solution is added to adjust the mixture to neutral, thereby obtaining a phenolic resin oligomer solution;

[0009] The water in the phenolic resin oligomer solution is evaporated, then a low-carbon alcohol is added, and a phenolic low-carbon alcohol solution is prepared; wherein the low-carbon alcohol includes any one of methanol, ethanol, propanol, and butanol;

[0010] In a silicate solution, a second acid solution or a second alkali solution is added, and the pH value of the silicate solution is adjusted to be between 4.0-10.0, thereby preparing a silica sol; the silica sol includes colloidal silica particles, wherein the particle size of the silica particles is controlled by adjusting the pH value;

[0011] The phenolic low-carbon alcohol solution and the silica sol are mixed and stirred at 35-45℃ to obtain a mixture, and the mixture is washed, filtered, and dried, thereby obtaining a silica-phenolic resin composite carbon source; wherein the silica particles are uniformly dispersed in the silica-phenolic resin composite carbon source;

[0012] Under an inert atmosphere, the silica-phenolic resin composite carbon source is subjected to carbonization treatment, thereby obtaining a carbonized product with a carbon skeleton and a SiO2 template; wherein the carbon skeleton is a three-dimensional continuous carbon skeleton formed by pyrolysis of the phenolic resin oligomer, and constitutes a continuous conductive network; the SiO2 particles are uniformly dispersed between the carbon skeleton as a template.

[0013] The carbonization product is subjected to wet etching treatment with an etching solution, through the wet etching treatment, the SiO2 template is selectively etched away, thereby forming a hole at the position occupied by the SiO2 particle, and then washing, filtering and drying to obtain the porous carbon material with adjustable pore size.

[0014] Preferably, the phenol source includes one of phenol, resorcinol, phloroglucinol, cardanol, m-aminophenol, 3-amino phenol, cresol, nonyl phenol, octyl phenol and dimethyl phenol;

[0015] The aldehyde source solution includes one or more of formaldehyde, p-xylylene glycol, acetaldehyde and furfural;

[0016] The first alkali solution includes one of sodium hydroxide solution, potassium hydroxide solution and ammonia solution;

[0017] The first acid solution includes one of sulfuric acid solution, hydrochloric acid solution, nitric acid solution, acetic acid solution and citric acid solution;

[0018] The silicate solution includes one of sodium silicate solution or potassium silicate solution;

[0019] The second alkali solution includes one of sodium hydroxide solution, potassium hydroxide solution and ammonia solution;

[0020] The second acid solution includes one of sulfuric acid solution, hydrochloric acid solution and nitric acid solution;

[0021] The etching solution includes one of HF solution, NaOH solution or KOH solution.

[0022] Preferably, the first acid solution is added to adjust the mixed solution to neutral, specifically, the first acid solution is added to adjust the mixed solution to pH = 7.0 ± 0.5.

[0023] Preferably, the water in the phenolic aldehyde resin oligomer solution is evaporated, and then a low-carbon alcohol is added to prepare a phenolic aldehyde low-carbon alcohol solution, which specifically includes:

[0024] The water in the phenolic aldehyde resin oligomer solution is evaporated by any one of rotary evaporation, reduced pressure evaporation, water bath evaporation or hot plate evaporation;

[0025] The low-carbon alcohol is added in a proportion that the mass concentration of the phenolic aldehyde resin oligomer in the phenolic aldehyde low-carbon alcohol solution is 20-30 wt.%, to prepare the phenolic aldehyde low-carbon alcohol solution.

[0026] Preferably, the execution sequence of preparing the silica sol and the phenolic low-carbon alcohol solution includes: preparing the silica sol first, then preparing the phenolic low-carbon alcohol solution; or simultaneously preparing the silica sol and the phenolic low-carbon alcohol solution; or preparing the phenolic low-carbon alcohol solution first, then preparing the silica sol.

[0027] Preferably, the carbonization treatment includes: increasing the temperature from room temperature to 600-900℃ at a temperature increasing rate of 2-10℃ / min, and keeping the temperature for 1-8 hours.

[0028] Preferably, the method of wet etching the carbonization product by using the etching solution includes: immersing the carbonization product in the etching solution to perform the wet etching treatment.

[0029] The washing is washing to neutral by using deionized water.

[0030] The drying temperature is 80-110℃.

[0031] Further preferably, the method of wet etching the carbonization product by using the etching solution further includes: performing magnetic stirring while immersing, and the time is 0.5-24 hours.

[0032] In the second aspect, the embodiment of the present application provides a porous carbon material with adjustable pore size, which is prepared by the preparation method of the first aspect.

[0033] In the third aspect, the embodiment of the present application provides an application of the porous carbon material with adjustable pore size, which is prepared by the preparation method of the first aspect, and the porous carbon material is used in an electrode material, a separator material or a coating material of a secondary battery.

[0034] The preparation method of the porous carbon material with adjustable pore size provided by the embodiment of the present application successfully constructs a porous carbon material with a three-dimensional continuous carbon skeleton and an adjustable pore size structure, by generating a silica sol with adjustable particle size under a controllable pH condition, and uniformly compounding the silica sol with a phenolic resin oligomer in a low-carbon alcohol system, and then performing carbonization and template etching. The method has a simple process flow and mild preparation conditions, avoids problems such as poor dispersibility and non-uniform pore structure of a traditional solid template, improves the controllability of the pore size, and also significantly improves the specific surface area of the porous carbon material, facilitates the rapid diffusion and effective storage of metal ions, and thus effectively improves the electrochemical performance of the porous carbon material in an energy storage device, and has good controllability and industrial application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The flow chart of the preparation method of the porous carbon material with adjustable pore size provided by the embodiment of the present application is shown in the figure.

[0036] Figure 2 A scanning electron microscope (SEM) image of the porous carbon material with adjustable pore size prepared in Example 1 of the present application;

[0037] Figure 3 A pore size distribution graph of the porous carbon material with adjustable pore size prepared in Example 1 of the present application;

[0038] Figure 4 A pore size distribution graph of the porous carbon material prepared in Comparative Example 1 of the present application;

[0039] Figure 5 A pore size distribution graph of the porous carbon material prepared in Comparative Example 2 of the present application;

[0040] Figure 6 A pore size distribution graph of the porous carbon material prepared in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0041] The technical solutions of the present application are described in further detail below with reference to the accompanying drawings and examples.

[0042] The present application provides a porous carbon material with adjustable pore size and a preparation method thereof.

[0043] Figure 1 A flow chart of the preparation method of the porous carbon material with adjustable pore size provided in the present application is shown below, which is first described in combination with Figure 1 the preparation method proposed in the present application.

[0044] As Figure 1 the main steps of the preparation method of the porous carbon material with adjustable pore size include:

[0045] Step 110: adding a phenol source into a container at 25-50℃, then adding a first alkali solution to stir, then increasing the temperature to 60-90℃, then adding an aldehyde source solution to stir, and finally cooling to room temperature, adding a first acid solution to adjust the mixed solution to neutral, to obtain a phenolic aldehyde resin oligomer solution.

[0046] The phenol source includes one of phenol, resorcinol, phloroglucinol, cardanol, m-aminophenol, 3-amino phenol, cresol, nonyl phenol, octyl phenol, and dimethyl phenol;

[0047] The aldehyde source solution includes one or more of formaldehyde, p-xylylene glycol, acetaldehyde, and furfural;

[0048] The first alkali solution includes one of a sodium hydroxide solution, a potassium hydroxide solution, and an ammonia water solution;

[0049] The first acid solution includes one of a sulfuric acid solution, a hydrochloric acid solution, a nitric acid solution, an acetic acid solution, and a citric acid solution;

[0050] The first acid solution is added to adjust the mixture to neutral, specifically, the pH of the mixture is adjusted to 7.0±0.5 after adding the first acid solution.

[0051] In this step, first, under alkaline conditions, the phenol source and the aldehyde source solution (using formaldehyde as an example) undergo nucleophilic addition reaction to form a hydroxymethyl phenol intermediate, and then further condensation reaction occurs to form a phenolic aldehyde resin oligomer with a certain degree of polymerization. By controlling the temperature and reaction time, the condensation degree can be effectively adjusted to obtain a liquid oligomeric phenolic aldehyde resin system suitable for subsequent compounding. After the reaction is completed, the pH is adjusted to neutral by adding an acid solution to terminate the reaction and stabilize the obtained phenolic aldehyde resin oligomer solution.

[0052] Preferably, the stirring time after adding the first alkali solution is 10-30 min, and the temperature is preferably 40-50°C to fully alkalize the system. Too low temperature can cause partial precipitation or uneven dispersion of the phenol source, which is not conducive to dispersion. Too high temperature may induce condensation reaction to form unstable intermediate polymers.

[0053] Preferably, the aldehyde source solution can be added in a slow dropwise manner, and the reaction is maintained at a temperature of 60-90°C for 60-120 min to promote the condensation reaction. Finally, the first acid solution is added to adjust the pH of the mixture to neutral. Optionally, continue to stir for 10-20 min after adding the first acid solution to terminate the reaction and achieve stability.

[0054] It should be noted that the reaction time can be adjusted according to the amount of reactants. When the concentration of reactants is high, the effective collision frequency in the system increases, and the reaction rate is relatively fast, so the reaction time can be appropriately shortened. However, the viscosity of the system increases, which may cause diffusion limitation in the later condensation process, and the temperature and target polymerization degree need to be controlled comprehensively. Conversely, when the concentration of reactants is low, the reaction rate decreases, and in order to ensure sufficient condensation, the reaction time should be appropriately extended. Therefore, there is a certain corresponding relationship between the reaction time and the concentration of reactants. Those skilled in the art can optimize the setting according to the actual system parameters combined with common technical means in the art in actual implementation.

[0055] Step 120, evaporate the water in the phenolic aldehyde resin oligomer solution, and then add a low-carbon alcohol to prepare a phenolic aldehyde low-carbon alcohol solution;

[0056] Specifically, the water evaporation can be any one of rotary evaporation, reduced pressure evaporation, water bath evaporation, or hot plate evaporation.

[0057] The added low-carbon alcohol includes any one of methanol, ethanol, propanol, and butanol; the added amount of low-carbon alcohol is in a proportion of 20-30 wt.% of the mass concentration of the phenolic resin oligomer in the phenolic low-carbon alcohol solution after being added.

[0058] If the mass concentration of the phenolic resin oligomer in the phenolic low-carbon alcohol solution exceeds 30 wt.%, the viscosity of the solution will significantly increase, and further cross-linking reactions between the phenolic resin oligomers are prone to occur when the solution is compounded with the silica sol, so that the system quickly gels, thereby being not conducive to the uniform doping and dispersion of the silica particles, and possibly affecting the uniformity of the composite structure and the regulation of the pore structure. On the contrary, if the mass concentration of the phenolic resin oligomer is less than 20 wt.%, the carbon precursor content will be insufficient, it will be difficult to form a complete three-dimensional continuous carbon skeleton structure after carbonization, and the coating degree of the silica template will be reduced, which will cause the pore structure to collapse, the pore wall to be discontinuous, or the electrical conductivity to be reduced, thereby weakening the mechanical strength and electrochemical performance of the final porous carbon material. Therefore, in the present application, the mass concentration of the phenolic resin oligomer is preferably controlled at 20-30 wt.% to balance the dispersibility, structural integrity, and the construction of the conductive network, and to ensure that a porous carbon material with good pore structure regulation ability and performance is obtained.

[0059] Step 130, a second acid solution or a second base solution is added to the silicate solution to adjust the pH value of the silicate solution to be between 4.0 and 10.0, and a silica sol is configured.

[0060] Specifically, the silica sol includes colloidal silica particles.

[0061] The silicate solution includes one of a sodium silicate solution or a potassium silicate solution;

[0062] The second base solution includes one of a sodium hydroxide solution, a potassium hydroxide solution, and an ammonia water solution;

[0063] The second acid solution includes one of a sulfuric acid solution, a hydrochloric acid solution, and a nitric acid solution.

[0064] In this step, the particle size of the silica particles is controlled by adjusting the pH value, which is further explained as follows:

[0065] In the present application, by introducing a second acid solution or a second base solution into the silicate solution, the pH of the system is adjusted to be within the range of 4.0-10.0, which can induce the hydrolysis and condensation reactions of silicates, thereby forming a colloidal silica sol. This process mainly includes the hydrolysis of silicate ions to generate monomeric silicic acid and subsequent polycondensation reactions to generate a stable Si-O-Si bond network structure, gradually forming nanoscale colloidal particles.

[0066] The hydrolysis and condensation rates are significantly different under different pH conditions, thereby affecting the growth mechanism and particle size distribution of the silica particles. Under the slightly acidic conditions (pH = 4-6), the hydrolysis rate is relatively fast, and the condensation rate is relatively slow, which is conducive to the formation of colloidal particles with small particle size and good dispersibility; under the neutral or slightly alkaline conditions (pH = 7-10), the condensation rate is accelerated, the colloidal particle size gradually increases, and the interaction between the particles is enhanced, which is easy to form SiO2 particles with large size or more compact structure.

[0067] Therefore, in actual implementation, the target pH value to be regulated can be determined according to the actual needs of the pore size, so as to realize the controllable regulation of the silica particle size, and lay a foundation for the subsequent regulation of the pore size of the porous carbon material.

[0068] The execution sequence of the above steps 110-120 and step 130 can be performed in any order or synchronously, that is, the execution sequence of configuring the silica sol and preparing the phenolic low-alcohol solution includes: first configuring the silica sol and then preparing the phenolic low-alcohol solution, or synchronously configuring the silica sol and preparing the phenolic low-alcohol solution, or first preparing the phenolic low-alcohol solution and then preparing the silica sol.

[0069] In step 140, the phenolic low-alcohol solution and the silica sol are mixed and stirred at 35-45°C to obtain a mixture, and the mixture is washed, filtered and dried to obtain a silica-phenolic resin composite carbon source.

[0070] In this step, the phenolic low-alcohol solution and the silica sol are mixed and stirred at 35-45°C to obtain a mixture, so that the phenolic oligomers are adsorbed to the surface of the silica by hydrogen bonding or van der Waals force, and part of the phenolic molecules penetrate into the gap between the sol particles to form a composite structure. In this process, no significant chemical cross-linking reaction occurs in the system, and after washing, filtering and drying treatment, a silica-phenolic resin composite carbon source with good dispersibility and interfacial bonding force is formed. In the silica-phenolic resin composite carbon source, the silica particles are uniformly dispersed.

[0071] The uniform dispersion of the silica particles is mainly due to the following two aspects: first, the particles in the silica sol are in a colloidal state, the particle size is controllable in the previous configuration process and has a surface charge, and has high dispersion stability and is not easy to agglomerate; second, the hydroxyl groups in the phenolic oligomers can form physical adsorption with the surface of the silica by hydrogen bonding or van der Waals force, so as to realize the "coated" distribution and stable fixation of the silica particles during the mixing and stirring process, and avoid the aggregation thereof. Therefore, the silica maintains a high uniform spatial distribution, which provides a basis for the uniformity of the pore size distribution after subsequent carbonization and etching.

[0072] Step 150, carbonizing the silica-phenolic resin composite carbon source under an inert atmosphere to obtain a carbonized product with a carbon skeleton and SiO2 template;

[0073] The carbon skeleton is a three-dimensional continuous carbon skeleton formed by pyrolysis of the phenolic resin oligomer and constitutes a continuous conductive network; the SiO2 particles are uniformly dispersed between the carbon skeleton as a template.

[0074] The carbonization process includes: heating from room temperature to 600-900℃ at a heating rate of 2-10℃ / min, and holding for 1-8 hours.

[0075] By controlling the heating rate at 2-10℃ / min, this step can effectively avoid material structure damage caused by local thermal stress, and ensure that the phenolic resin oligomer slowly releases small molecular substances (such as H2O, CO2, CH4, etc.) during pyrolysis, gradually converting into carbonaceous materials. The controllable heating process helps to form a stable carbon skeleton structure, while reducing agglomeration or cracking during thermal polycondensation.

[0076] During the process of holding the temperature at 600-900℃ for 1-8 hours, the phenolic oligomer completes the transformation from amorphous organic structure to amorphous carbon structure with low graphitization degree, forming a three-dimensional continuous conductive carbon skeleton with good electronic conductivity.

[0077] During the entire carbonization process, the SiO2 particles are uniformly embedded in the carbon skeleton as a hard template and do not participate in the pyrolysis reaction, maintaining the original particle size and dispersion state, ensuring that the pores formed after subsequent etching are consistent in size and distribution, thereby obtaining a porous carbon material with uniform pore size and high specific surface area.

[0078] Step 160, wet etching the carbonized product with an etching solution to selectively etch away the SiO2 template, thereby forming pores at the location occupied by the SiO2 particles, and then washing, filtering, and drying to obtain a porous carbon material with adjustable pore size.

[0079] The method of wet etching the carbonized product with an etching solution includes: immersing the carbonized product in the etching solution for wet etching treatment; preferably, magnetic stirring can also be performed simultaneously, and the uniformly dispersed SiO2 template in the carbonized product is selectively removed by wet etching to form a regular pore structure at its original location, obtaining a porous carbon material with adjustable pore size.

[0080] Specifically, the etching solution can be selected from any one of a hydrofluoric acid (HF) solution, a sodium hydroxide (NaOH) solution or a potassium hydroxide (KOH) solution. Among them, the HF solution can directly react with SiO2 to generate soluble hexafluorosilicic acid (H2SiF6); the alkali solution such as NaOH or KOH can convert SiO2 into soluble silicate through reaction, thereby realizing efficient etching of the SiO2 template.

[0081] The wet etching treatment method includes fully immersing the carbonization product in the etching solution, preferably under magnetic stirring for 0.5-24 hours. The magnetic stirring can further enhance the contact efficiency of the etching solution and the carbonization product, and accelerate the removal reaction process of the SiO2 template.

[0082] After the etching is completed, the obtained porous carbon material is repeatedly washed with deionized water until the washing liquid is neutral, so as to remove residual etching by-products. After the washing is completed, drying is performed at a temperature of 80-110°C, and the drying time is preferably 6-12 hours, so as to fully remove the adsorbed water, maintain the stability of the pore structure of the material, and prevent thermal collapse.

[0083] The porous carbon material with adjustable pore size prepared by the above preparation method has a main pore size distribution of 0.5-100 nm. The smaller the pH value of the silicate solution in step 130 is, the smaller the main pore size of the obtained porous carbon material is. The larger the pH value is, the larger the main pore size of the obtained porous carbon material is. The prepared porous carbon material can be applied to electrode materials, separator materials or coating materials of secondary batteries.

[0084] Summarizing the above process, taking phenol, formaldehyde and sodium silicate as examples of the phenol source, the aldehyde source solution and the silicate, the mechanism of the pore size regulation of the present application is as follows:

[0085] The phenol can undergo addition reaction with formaldehyde under alkaline conditions, followed by condensation and polycondensation reactions. When the sodium silicate (Na2SiO3) solution is added with acid, hydrolysis reaction occurs. In this reaction, the sodium silicate combines with hydrogen ions (H + ) in water to generate silicic acid (H2SiO3) and corresponding salt. Here, the H + comes from the acid, which combines with silicate ions (SiO3 2- ) in sodium silicate to form silicic acid (H2SiO3) that is insoluble in water. Since the solubility of silicic acid in water is very small, it is easy to precipitate from the solution in the form of a precipitate. This precipitate is silicon dioxide (SiO2), but usually exists in a hydrated form, such as SiO2·nH2O (where n represents the number of water molecules). In water, sodium silicate can completely ionize into metasilicate ions (SiO3 2- ) and sodium ions (Na +), under alkaline conditions, sodium silicate undergoes hydrolysis with water to form silicic acid (H2SiO3) and sodium hydroxide (NaOH). Due to the high concentration of hydroxide ions (OH - ) under alkaline conditions, it inhibits the further hydrolysis of silicic acid (H2SiO3), causing the reaction to proceed in the reverse direction, i.e., towards the formation of sodium silicate (Na2SiO3).

[0086] The particle size of the silica produced by the hydrolysis of sodium silicate solution changes with the increase of pH value. Specifically, when the pH value is low (such as under acidic conditions), the hydrolysis reaction of sodium silicate is fast, but the generated silica particles are small. This is because the high concentration of hydrogen ions under acidic conditions promotes the combination of silicate ions and hydrogen ions, but also accelerates the condensation and precipitation process of silicic acid, resulting in small particles. With the increase of pH value (such as under alkaline conditions), the hydrolysis rate of sodium silicate slows down, and the generated silica particles gradually increase in size. This is because under alkaline conditions, the concentration of hydroxide ions increases, which combine with silicate ions to form more stable silicate ions, thus slowing down the condensation and precipitation speed of silicic acid. In summary, the particle size of the silica produced by the hydrolysis of sodium silicate solution gradually increases with the increase of pH, but the specific change trend and degree depend on the combined action of multiple factors. The reaction principle of synthesizing porous carbon involves complex chemical reactions and physical processes, such as material ratio and preparation process. By fine control of the synergistic effect of various factors, porous carbon materials with adjustable pore size and excellent performance can be prepared.

[0087] In the present invention, silica sol is generated by the hydrolysis of sodium silicate solution as a hard template, replacing the traditional solid silica particles synthesized by gas phase method, effectively overcoming the problems of poor dispersion and easy agglomeration of the latter in the composite process, significantly improving the uniformity and stability of the system. The method is simple and easy to control, with strong process feasibility. By adjusting the pH value of the solution to 4.0-10.0, the particle size distribution of silica in the hydrolysis process can be precisely controlled, so that different pore structures can be realized after carbonization, and porous carbon materials with high specific surface area and hierarchical pore structure can be obtained. Since the silica can be uniformly deposited in the phenolic carbon precursor system in the sol state, the aggregation problem of nano-SiO2 template in the carbonization process is avoided, so that the pore distribution formed after etching treatment is more uniform, which is beneficial to the construction of ion / electrolyte diffusion and rapid transmission channels.

[0088] In summary, the method not only improves the controllability and repeatability of the structure of the porous carbon material, but also is beneficial to improving the specific capacity, rate performance and cycle stability of the porous carbon material in electrochemical applications, and has broad application prospects.

[0089] In order to make the purposes, technical solutions and advantages of the present application clearer, further detailed description will be made to the present application with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall into the protection scope of the present application.

[0090] Embodiment 1

[0091] The present embodiment provides a preparation method of a porous carbon material with adjustable pore size, which specifically comprises the following steps:

[0092] Step 1, 8 g of melted phenol is added into a three-necked flask at 45℃, then 10 mL of 0.2M NaOH solution is added, and stirred for 20 min to mix uniformly; then 13.76 g of formaldehyde solution (37 wt.%) is slowly added dropwise, and stirred at 78℃ for 60 min to obtain a reaction product; the reaction product is cooled to room temperature, and then 0.2M HCl aqueous solution is used to adjust the pH to neutral (pH = 7.0±0.5), and continue to stir for 15 min to obtain a phenolic resin oligomer solution;

[0093] Step 2, the phenolic resin oligomer solution prepared in step 1 is subjected to rotary evaporation to evaporate the water in the solution, and then ethanol is added to prepare a phenolic ethanol solution with a phenolic mass concentration of 20 wt.%;

[0094] Step 3, 7.5 g of sodium silicate (SiO2 27 wt.%), 22.5 g of water and appropriate amount of 0.50M H2SO4 aqueous solution are mixed, the pH value of the sodium silicate solution is adjusted to 4.0 by the H2SO4 aqueous solution, and stirred at room temperature for 30 min to form a silica sol with colloidal silica particles;

[0095] Step 4, the silica sol with a pH value of 4.0 prepared in step 3 is added into 10 g of the phenolic ethanol solution obtained in step 2 at 40℃, and stirred for 1 h, then vacuum filtration is performed, and washed with deionized water for 3 times until the washing liquid is neutral, and dried at 100℃ for 10 h to obtain a silica-phenolic resin composite carbon source;

[0096] Step 5, the silica-phenolic resin composite carbon source obtained in step 4 is carbonized in a tube furnace, nitrogen gas is passed, the nitrogen gas flow rate is 5 L / min, the temperature is raised at a rate of 5℃ / min from room temperature to 800℃, and kept at this temperature for 2 h to obtain a carbonized product;

[0097] Step 6, the carbonized product is subjected to wet etching with hydrofluoric acid, and magnetically stirred for 24 h, then repeatedly washed with deionized water until the washing liquid is neutral, and dried at 80℃ for 8 h to finally obtain a finished porous carbon material with adjustable pore size.

[0098] The scanning electron microscope (SEM) image of the porous carbon material with adjustable pore size prepared in this embodiment is shown in Figure 2 The pore size distribution graph of the porous carbon material with adjustable pore size is shown in Figure 3

[0099] Embodiment 2

[0100] The embodiment provides a preparation method of a porous carbon material with adjustable pore size, and specifically comprises the following steps:

[0101] Step 1, 8 g of melted phenol is added into a three-necked flask at 45°C, and then 10 mL of 0.2M NaOH solution is added, and stirred for 20 min to mix uniformly; then 13.76 g of formaldehyde solution (37 wt.%) is slowly added dropwise, and stirred at 78°C for 60 min to obtain a reaction product; the reaction product is cooled to room temperature, and then 0.2M HCl aqueous solution is used to adjust the pH to neutral (pH = 7.0±0.5), and continue to stir for 15 min to obtain a phenolic resin oligomer solution;

[0102] Step 2, the phenolic resin oligomer solution prepared in step 1 is evaporated by a rotary evaporation method, and then ethanol is added to prepare a phenolic ethanol solution with a phenolic mass concentration of 20 wt.%;

[0103] Step 3, 7.5 g of sodium silicate (Si O2 27 wt.%), 22.5 g of water and appropriate amount of 0.50M H2SO4 aqueous solution are mixed, the pH value of the sodium silicate solution is adjusted to 5.0 by the H2SO4 aqueous solution, and stirred at room temperature for 30 min to form a silica sol with colloidal silica particles;

[0104] Step 4, the silica sol with a pH value of 5.0 prepared in step 3 is added into 10 g of the phenolic ethanol solution obtained in step 2 at 40°C, and stirred for 1 h, and then vacuum filtration is performed, and washed with deionized water for 3 times until the washing liquid is neutral, and dried at 100°C for 10 h to obtain a silica-phenolic resin composite carbon source;

[0105] Step 5, the silica-phenolic resin composite carbon source obtained in step 4 is carbonized in a tube furnace, nitrogen gas is passed, the nitrogen gas flow is 5 L / min, the heating rate is 5°C / min, the temperature is increased from room temperature to 800°C, and the temperature is kept at 800°C for 2 h to obtain a carbonized product;

[0106] Step 6, the carbonized product is wet etched by hydrofluoric acid, and magnetically stirred for 24 h, and then repeatedly washed with deionized water until the washing liquid is neutral, and dried at 80°C for 8 h to finally obtain the finished porous carbon material with adjustable pore size.

[0107] Embodiment 3

[0108] ​The embodiment provides a preparation method of a pore size adjustable porous carbon material, and specifically comprises the following steps:

[0109] Step 1, 8g of melted phenol is added into a three-necked flask at 45 DEG C, then 10mL of 0.2M NaOH solution is added, and stirring is conducted for 20min until the mixture is uniformly mixed; then 13.76g of formaldehyde solution (37wt.%) is slowly added dropwise, stirring is conducted at 78 DEG C for 60min to obtain a reactant, the reactant is cooled to room temperature, 0.2M HCl aqueous solution is used to adjust the pH value to neutral (pH=7.0+ / -0.5), and stirring is continuously conducted for 15min to obtain a phenolic aldehyde resin oligomer solution;

[0110] Step 2, the phenolic aldehyde resin oligomer solution prepared in step 1 is subjected to a rotary evaporation method, water in the solution is evaporated, then ethanol is added, and a phenolic aldehyde ethanol solution with a phenolic aldehyde mass concentration of 20wt.% is prepared;

[0111] Step 3, 7.5g of sodium silicate (Si O2 27wt.%), 22.5g of water and appropriate amount of 0.50M NaOH aqueous solution are mixed, the pH value of the sodium silicate solution is adjusted to 8.0 through the NaOH aqueous solution, and stirring is conducted at room temperature for 30min to form a silica sol with colloidal silica particles;

[0112] Step 4, the silica sol with a pH value of 8.0 prepared in step 3 is added into 10g of the phenolic aldehyde ethanol solution obtained in step 2 at 40 DEG C, stirring is conducted for 1h, then vacuum filtration is conducted, washing is conducted with deionized water for 3 times until the washing liquid is neutral, and drying is conducted at 100 DEG C for 10h, so that a silica-phenolic aldehyde resin composite carbon source is obtained;

[0113] Step 5, the silica-phenolic aldehyde resin composite carbon source obtained in step 4 is carbonized in a tube furnace, nitrogen gas is passed, the nitrogen gas flow is 5L / min, the temperature is raised at a rate of 5 DEG C / min from room temperature to 800 DEG C, and the temperature is kept at the temperature for 2h, so that a carbonization product is obtained;

[0114] Step 6, the carbonization product is subjected to wet etching through hydrofluoric acid, magnetic stirring is conducted for 24h, then repeated washing is conducted with deionized water until the washing liquid is neutral, and drying is conducted at 80 DEG C for 8h, so that a pore size adjustable finished product porous carbon material is finally obtained.

[0115] Embodiment 4

[0116] The embodiment provides a preparation method of a pore size adjustable porous carbon material, and specifically comprises the following steps:

[0117] Step 1, 8 g of melted phenol was added into a three-necked flask at 45℃, then 10 mL of 0.2 M NaOH solution was added, and stirred for 20 min to mix evenly; then 13.76 g of formaldehyde solution (37 wt.%) was slowly added dropwise, and stirred at 78℃ for 60 min to obtain a reaction product; the reaction product was cooled to room temperature, and the pH was adjusted to neutral (pH = 7.0 ± 0.5) with 0.2 M HCl aqueous solution, and stirring was continued for 15 min to obtain a phenolic oligomer solution;

[0118] Step 2, the phenolic oligomer solution prepared in step 1 was subjected to rotary evaporation to evaporate the water in the solution, and then ethanol was added to prepare a phenolic ethanol solution with a phenolic mass concentration of 20 wt.%;

[0119] Step 3, 7.5 g of sodium silicate (SiO2 27 wt.%), 22.5 g of water, and an appropriate amount of 0.50 M NaOH aqueous solution were mixed, and the pH of the sodium silicate solution was adjusted to 9.0 by the NaOH aqueous solution, and stirred at room temperature for 30 min to form a silica sol with colloidal silica particles;

[0120] Step 4, the silica sol with a pH of 9.0 prepared in step 3 was added to 10 g of the phenolic ethanol solution obtained in step 2 at 40℃, and stirred for 1 h, then vacuum filtration was performed, and washed with deionized water for 3 times until the washing liquid was neutral, and dried at 100℃ for 10 h to obtain a silica-phenolic resin composite carbon source;

[0121] Step 5, the silica-phenolic resin composite carbon source obtained in step 4 was carbonized in a tube furnace, nitrogen was passed at a flow rate of 5 L / min, the temperature was raised at a rate of 5℃ / min from room temperature to 800℃, and the temperature was kept at 800℃ for 2 h to obtain a carbonized product;

[0122] Step 6, the carbonized product was subjected to wet etching with hydrofluoric acid, and stirred magnetically for 24 h, then washed repeatedly with deionized water until the washing liquid was neutral, and dried at 80℃ for 8 h to obtain a finished product of porous carbon material with adjustable pore size.

[0123] Example 5

[0124] The embodiment provides a preparation method of a porous carbon material with adjustable pore size, and specifically comprises the following steps:

[0125] Step 1, 8 g of phenol was added into a three-necked flask at 45℃, then 10 mL of 0.2 M NaOH solution was added, and stirred for 20 min to mix evenly; then 13.76 g of formaldehyde solution (37 wt.%) was slowly added dropwise, and stirred at 78℃ for 60 min to obtain a reaction product. After the reaction product was cooled to room temperature, 0.2 M HCl aqueous solution was used to adjust the pH to neutral (pH = 7.0 ± 0.5), and stirring was continued for 15 min to obtain a phenolic resin oligomer solution;

[0126] Step 2, the phenolic resin oligomer solution prepared in step 1 was subjected to rotary evaporation to evaporate the water in the solution, and then ethanol was added to prepare a phenolic ethanol solution with a phenolic mass concentration of 20 wt.%.

[0127] Step 3, 5.5 g of potassium silicate (SiO2 27 wt.%), 22.5 g of water, and an appropriate amount of 1 M HCl aqueous solution were mixed, and the pH value of the potassium silicate solution was adjusted to 4.5 by the HCl aqueous solution. The solution was stirred at room temperature for 30 min to form a silica sol with colloidal silica particles.

[0128] Step 4, the silica sol with a pH value of 4.5 prepared in step 3 was added to 10 g of the phenolic ethanol solution obtained in step 2 at 40℃, and stirred for 1 h, followed by vacuum filtration, washing with deionized water for 3 times until the washing liquid was neutral, and drying at 100℃ for 10 h to obtain a silica-phenolic resin composite carbon source.

[0129] Step 5, the silica-phenolic resin composite carbon source obtained in step 4 was carbonized in a tube furnace, nitrogen was passed at a flow rate of 5 L / min, the temperature was raised at a rate of 5℃ / min from room temperature to 800℃, and the temperature was kept at 800℃ for 2 h to obtain a carbonized product.

[0130] Step 6, the carbonized product was subjected to wet etching with hydrofluoric acid, and stirred magnetically for 24 h, then washed repeatedly with deionized water until the washing liquid was neutral, and dried at 80℃ for 8 h to obtain a final product of porous carbon material with adjustable pore size.

[0131] Comparative Example 1

[0132] The execution method of this comparative example was basically the same as that of Example 1, except that sodium silicate in step 3 was replaced by sodium metasilicate.

[0133] The pore size distribution graph of the porous carbon material prepared in Comparative Example 1 is shown in Figure 4 .

[0134] Comparative Example 2

[0135] The execution method of this comparative example was basically the same as that of Example 1, except that the sulfuric acid aqueous solution in step 3 was replaced by acetic acid aqueous solution.

[0136] The pore size distribution of the porous carbon material prepared in Comparative Example 2 is shown in FIG. 2. Figure 5

[0137] Comparative Example 3

[0138] The method of performing the present comparative example is substantially the same as that of Example 1, except that step 3 is not performed, and in step 4, nano-silica (particle size of about 7 nm) prepared by gas phase deposition using a conventional method is directly added to 10 g of the phenolic alcohol solution obtained in step 2 at 40°C.

[0139] The pore size distribution of the porous carbon material prepared in Comparative Example 3 is shown in FIG. 3. Figure 6

[0140] The products prepared in Examples 1-5 and Comparative Examples 1-3 were tested for specific surface area, pore size and pore volume using the static volumetric nitrogen adsorption method, and the test results are shown in Table 1.

[0141] Table 1 is the test results of Examples 1-5 and Comparative Examples 1-3.

[0142]

[0143]

[0144] As can be seen from Table 1, a comparison of Comparative Example 3 and Examples 1-5 shows that using a silica sol obtained by hydrolysis of a silicate solution as a template can obtain a porous carbon material with a larger specific surface area.

[0145] As can be seen from Figure 3 (Example 1) and Figure 6 (Comparative Example 3), using a silica sol (Example 1) added with a silicate as a hard template to prepare a porous carbon material has a uniform pore size distribution, avoiding the phenomenon of easy agglomeration between nano-silica particles due to strong van der Waals forces during dispersion of a conventional silica template, which causes uneven pore size distribution. The silica sol avoids such problems due to its low concentration, ensuring uniform dispersion of silica particles in the carbon matrix, thereby ensuring the concentration of the pore size distribution of the porous carbon material.

[0146] As can be seen from Figure 3 (Example 1) and Figure 4 (Comparative Example 1), metasilicate (Comparative Example 1) is a dimer or trimer of silicate, and the hydrolysis process is slow, resulting in larger and uneven silica particles, which leads to uneven pore size distribution of the subsequent porous carbon material.

[0147] ​​As can be seen from the data of Comparative Example 2 and Example 1 in Table 1, using a strong acid solution to provide hydrogen ions to provide an environment with a pH of 4-5 for the hydrolysis of sodium silicate can obtain a porous carbon material with a larger specific surface area. Compared with weak organic acids, strong acids are completely ionized in aqueous solution, resulting in faster hydrolysis of sodium silicate and smaller silica particles generated. This is because the high concentration of hydrogen ions promotes the combination of silicate ions and hydrogen ions, but also accelerates the condensation and precipitation process of silicic acid, resulting in smaller particles and thus increasing the pore volume of the carbon material.

[0148] As can be seen from the data of Comparative Example 2 and Example 1 in Table 1, using a strong acid solution to provide hydrogen ions to provide an environment with a pH of 4-5 for the hydrolysis of sodium silicate can obtain a porous carbon material with a larger specific surface area. Compared with weak organic acids, strong acids are completely ionized in aqueous solution, resulting in faster hydrolysis of sodium silicate and smaller silica particles generated. This is because the high concentration of hydrogen ions promotes the combination of silicate ions and hydrogen ions, but also accelerates the condensation and precipitation process of silicic acid, resulting in smaller particles and thus increasing the pore volume of the carbon material. Figure 3 Figure 5 As can be seen from the data of Comparative Example 2 and Example 1 in Table 1, using a strong acid solution to provide hydrogen ions to provide an environment with a pH of 4-5 for the hydrolysis of sodium silicate can obtain a porous carbon material with a larger specific surface area. Compared with weak organic acids, strong acids are completely ionized in aqueous solution, resulting in faster hydrolysis of sodium silicate and smaller silica particles generated. This is because the high concentration of hydrogen ions promotes the combination of silicate ions and hydrogen ions, but also accelerates the condensation and precipitation process of silicic acid, resulting in smaller particles and thus increasing the pore volume of the carbon material.

[0149] The preparation method of the porous carbon material with adjustable pore size provided by the embodiments of the present application generates silica sol with adjustable particle size by hydrolyzing silicate solution under controllable pH conditions, and uniformly composites with phenolic resin oligomers in a low carbon alcohol system, and successfully constructs the porous carbon material with a three-dimensional continuous carbon skeleton and an adjustable pore size structure through carbonization and template etching. The method has a simple process flow and mild preparation conditions, avoids the problems of poor dispersibility and non-uniform pore structure of traditional solid templates, improves the controllability of the pore size, and significantly improves the specific surface area of the porous carbon material, facilitating the rapid diffusion and effective storage of metal ions, thereby effectively improving the electrochemical performance of the porous carbon material in energy storage devices, and having good controllability and industrial application prospects.

[0150] The above specific embodiments further illustrate the purpose, technical solutions and advantages of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.​

Claims

1. A method for preparing porous carbon materials with tunable pore size, characterized in that, The preparation method includes: Add the phenol source to a container at 25-50℃, then add the first alkali solution and stir. Then raise the temperature to 60-90℃, add the aldehyde source solution and stir. Finally, cool to room temperature and add the first acid solution to adjust the mixture to neutral to obtain a phenolic resin oligomer solution. The water in the phenolic resin oligomer solution is evaporated, and then a low-carbon alcohol is added to prepare a phenolic low-carbon alcohol solution; wherein the low-carbon alcohol includes any one of methanol, ethanol, propanol, and butanol. A second acid solution or a second alkali solution is added to a silicate solution to adjust the pH value of the silicate solution to between 4.0 and 10.0, thereby preparing a silica sol; the silica sol comprises colloidal silica particles, wherein the particle size of the silica particles is controlled by adjusting the pH value. The phenolic low-carbon alcohol solution and the silica sol are mixed and stirred at 35-45°C to obtain a mixture. The mixture is then washed, filtered, and dried to obtain a silica-phenolic resin composite carbon source. In the silica-phenolic resin composite carbon source, the silica particles are uniformly dispersed. Under an inert atmosphere, the silica-phenolic resin composite carbon source is carbonized to obtain a carbonized product with a carbon skeleton and a SiO2 template; wherein, the carbon skeleton is a three-dimensional continuous carbon skeleton formed by the pyrolysis of phenolic resin oligomers, forming a continuous conductive network; and SiO2 particles are uniformly dispersed between the carbon skeleton as templates. The carbonized product is subjected to wet etching with an etching solution. Through the wet etching process, the SiO2 template is selectively etched away, thereby forming pores in the positions occupied by the SiO2 particles. After washing, filtering and drying, the porous carbon material with adjustable pore size is obtained.

2. The preparation method according to claim 1, characterized in that, The phenol source includes one of the following: phenol, resorcinol, phloroglucinol, cashew nut shell, m-aminophenol, 3-aminophenol, cresol, nonylphenol, octylphenol, and xylenol; The aldehyde source solution includes one or more of formaldehyde, terephthalaldehyde, acetaldehyde, and furfural; The first alkaline solution includes one of the following: sodium hydroxide solution, potassium hydroxide solution, and ammonia solution; The first acid solution includes one of the following: sulfuric acid solution, hydrochloric acid solution, nitric acid solution, acetic acid solution, and citric acid solution; The silicate solution includes either a sodium silicate solution or a potassium silicate solution. The second alkaline solution includes one of the following: sodium hydroxide solution, potassium hydroxide solution, and ammonia solution; The second acid solution includes one of the following: sulfuric acid solution, hydrochloric acid solution, and nitric acid solution; The etching solution includes one of the following: HF solution, NaOH solution, or KOH solution.

3. The preparation method according to claim 1, characterized in that, The step of adding the first acid solution to adjust the mixture to neutrality specifically involves adding the first acid solution to adjust the mixture to pH = 7.0 ± 0.

5.

4. The preparation method according to claim 1, characterized in that, The step of evaporating the water from the phenolic resin oligomer solution and then adding a low-carbon alcohol to prepare a phenolic low-carbon alcohol solution specifically includes: The water in the phenolic resin oligomer solution is evaporated using any one of the following evaporation methods: rotary evaporation, reduced pressure evaporation, water bath evaporation, or hot plate evaporation. The phenolic low-carbon alcohol solution was prepared by adding low-carbon alcohol at a ratio of 20-30 wt.% of the phenolic resin oligomer in the solution.

5. The preparation method according to claim 1, characterized in that, The execution order of preparing silica sol and preparing phenolic low-carbon alcohol solution includes: first preparing silica sol and then preparing phenolic low-carbon alcohol solution; or, preparing silica sol and preparing phenolic low-carbon alcohol solution simultaneously; or, preparing phenolic low-carbon alcohol solution first and then preparing silica sol.

6. The preparation method according to claim 1, characterized in that, The carbonization process includes: heating from room temperature to 600-900℃ at a heating rate of 2-10℃ / min, and holding at that temperature for 1-8 hours.

7. The preparation method according to claim 1, characterized in that, The method for wet etching the carbonized product using an etching solution includes: immersing the carbonized product in the etching solution and performing wet etching; The washing process involves using deionized water until the solution is neutral. The drying temperature is 80-110℃.

8. The preparation method according to claim 7, characterized in that, The method for wet etching the carbonized product using an etching solution further includes: magnetic stirring during immersion for 0.5-24 hours.

9. A porous carbon material with tunable pore size prepared by any one of the preparation methods described in claims 1-7.

10. An application of a porous carbon material with tunable pore size prepared by any one of the preparation methods according to claims 1-7, characterized in that, The porous carbon material is used in electrode materials, separator materials, or coating materials for secondary batteries.

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