A hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material and preparation method thereof

Abstract

The present invention discloses a hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material and its preparation method, belonging to the field of electrochemical energy storage material processing and application technology. The preparation method involves precuring and carbonizing a nanofiber filament / water-soluble resin wet gel prepared by a curing and crosslinking method in a tubular furnace to obtain the carbon aerogel electrode material in a single step. The hierarchical porosity of the carbon aerogel effectively improves the specific capacitance of the carbon aerogel compared to carbon aerogels with a single pore structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage material processing and application, and specifically relates to a hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material and a preparation method thereof. Background Art

[0002] Supercapacitors are a new type of green energy storage device, intermediate between traditional capacitors and batteries. With their high power density, rapid charge and discharge rates, wide operating temperature range, and excellent cycling stability, they have become one of the most promising electrochemical energy storage devices. Carbon aerogel supercapacitor electrode materials, among others, possess a rich porous structure, low density, high stability, high specific surface area, and high conductivity, enabling operation at high charge and discharge rates. However, their specific capacitance is often lower than that of activated carbon materials. Based on this, Baumann et al. investigated the effects of CO2 activation on the specific surface area and electrochemical properties of carbon aerogels. The results showed that CO2 activation effectively increased the micropores within the carbon aerogel particles and the macropores between the particles. Furthermore, the specific surface area of ​​the activated carbon aerogels was positively correlated with the activation time. Finally, a hierarchical porous carbon aerogel material was successfully prepared after 6 hours of activation, effectively improving the specific capacitance of the carbon aerogel. Liu et al. combined CO2 activation and KOH activation to activate and increase the pores of carbon aerogels. First, CO2 activation was used to activate a large number of micropores on the carbon nanoparticles of the carbon aerogels. Then, KOH activation was used to expand the micropores obtained above. Finally, they successfully prepared a porous carbon aerogel with a three-level pore size distribution. Its specific capacitance can reach 250F / g at a charge and discharge current density of 0.5A / g.

[0003] Patent CN104576084A proposes a method for preparing nanoporous carbon aerogel for supercapacitors, comprising the following steps: adding a 3.0-4.0×10 -2 mol / L of any of the following ionic solutions Al 3+ , Li + , Zn 2+ , Cu 2+ , Pb 2+The carbon aerogel powder is modified using the above-mentioned ion solution, so that the above-mentioned ions are deposited in the micropores of the carbon aerogel, thereby obtaining a nanoporous carbon aerogel for supercapacitors. Patent CN110379637A proposes a porous carbon aerogel fiber all-solid-state supercapacitor and a preparation method thereof. It proposes that graphene oxide / polyamic acid hydrogel is printed into a fibrous structure through a 3D printer, freeze-dried, thermally imidized, and carbonized to obtain a carbon aerogel fiber electrode, and finally assembled into a supercapacitor. Patent CN109321211A proposes a graphitized hierarchical porous carbon composite phase change energy storage material and a preparation method thereof, which includes using a low-cost carbon precursor, a graphitization catalyst, and a pore-forming agent as raw materials, and preparing graphitized hierarchical porous carbon through ball milling, carbonization, and other processes; then using the prepared graphitized hierarchical porous carbon as a supporting material and compounding it with a phase change material to obtain the graphitized hierarchical porous carbon composite phase change energy storage material. Patent CN113816356A proposes a five-step process for preparing hierarchical porous carbon aerogels, including liquefaction of biomass materials, preparation of organic hydrogels, solvent replacement, freeze-drying, and carbonization activation. First, wood powder and other biomass materials are liquefied to obtain a wood liquefaction precursor, which is then mixed with formaldehyde and hexamethylenetetramine and cross-linked at a certain temperature to form a hydrogel. After solvent replacement and drying, an aerogel is formed. Furthermore, by combining high-temperature pyrolysis and one-step water vapor activation technology, the properties of the aerogel are modified, the pore structure is adjusted, and a loose, porous, ultra-low-density, wood-based, all-component carbon aerogel is prepared.

[0004] The above research shows that the electrochemical performance of carbon aerogels can be effectively enhanced by constructing a hierarchical network structure through porous carbon aerogels. However, the preparation of carbon aerogel materials with hierarchical porous structures through activation and modification, which can be used to prepare supercapacitor electrode materials, is still understudied and the process is often time-consuming and complex. Summary of the Invention

[0005] In view of the above-mentioned problems existing in the prior art, the technical problem to be solved by the present invention is to provide a method for preparing a hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material, which utilizes the initial reaction stage and the aging penetration stage in the gel network formation process of the catalyst-catalyzed resin to construct a hierarchical network, and improves the strength of the gel network through a dual curing process (catalyst curing and heat curing), effectively reducing the gel shrinkage rate during the carbonization process, thereby conveniently preparing a high-porosity carbon aerogel. It is a fast, economical and simple method that overcomes the complexity of the existing carbon aerogel electrode material preparation technology and broadens the application field and application prospects of supercapacitor electrode materials. The present invention provides a hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material, which obtains a carbon aerogel electrode material in one step in a tubular furnace by pre-curing / carbonizing nanofiber filaments / water-soluble resin wet gel.

[0006] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0007] A method for preparing a hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material comprises precuring and carbonizing a nanofiber filament / water-soluble resin wet gel in a tubular furnace to obtain the carbon aerogel electrode material in one step. The method comprises the following steps:

[0008] (1) CNF dispersion was prepared by TEMPO oxidation method;

[0009] (2) mixing and dispersing the dispersion prepared in step (1) with the water-soluble resin solution, preparing a curing agent solution and deionized water in equal proportions to the water-soluble resin, slowly dropping them into the stirring solution, stirring continuously and then allowing the solution to stand for gelation, and placing the solution in an oven for aging to obtain a high-strength wet gel network;

[0010] (3) The wet gel sample obtained in step (2) is placed in a tubular furnace and heated in stages for pre-curing / carbonization to obtain a hierarchical porous carbon aerogel.

[0011] The method for preparing the hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material, the method for preparing the CNF dispersion in step (1) comprises: first weighing a wood fiber raw material and placing it in a blender, adding deionized water to disperse it evenly, then pouring it into a beaker, continuing to add deionized water, TEMPO catalyst and sodium bromide, stirring evenly, and then slowly adding NaClO solution, stirring at room temperature, and adjusting the pH value of the entire reaction system with NaOH solution to stabilize it at 9.5-10.5 until the reaction is completed; filtering the reaction solution with a sand core funnel and washing it with a large amount of deionized water to neutrality to obtain TEMPO-oxidized cellulose; finally preparing a TEMPO-oxidized cellulose suspension, pouring it into a high-pressure homogenizer and circulating homogenizing it at a pressure of 100 MPa to obtain a CNF dispersion; the concentration of the TEMPO-oxidized cellulose suspension is 0.5wt%-1wt%, and the concentration of the CNF dispersion is 2wt%-3wt%.

[0012] The preparation method of the hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material, the water-soluble resin and the corresponding curing agent in step (2) are specifically as follows: when the water-soluble resin is a water-soluble phenolic resin, the corresponding curing agent is an inorganic or organic medium-strong acid; when the water-soluble resin is a water-soluble epoxy resin, the corresponding curing agent is an aliphatic diamine, an aliphatic polyamine, an aromatic polyamine, a nitrogen-containing compound, a modified aliphatic amine, an organic acid, an acid anhydride, boron trifluoride and its complex; when the water-soluble resin is a water-soluble melamine formaldehyde resin or a water-soluble urea formaldehyde resin, the corresponding curing agent is sulfuric acid, hydrochloric acid, formic acid, ammonium chloride or ammonium sulfate; when the water-soluble resin is a water-soluble unsaturated When the water-soluble resin is a polyester resin, the corresponding curing agent is cyclohexanone peroxide, dibenzoyl peroxide or methyl ethyl ketone peroxide; when the water-soluble resin is a water-soluble polyurethane resin solution, the corresponding curing agent is toluene diisocyanate, trimethylolpropane or biuret polyisocyanate; when the water-soluble resin is a water-soluble acrylic resin solution, the corresponding curing agent is isocyanate, pyridine, amino resin, epoxy group-containing resin, tetraisopropoxy titanium, polyvinyl alcohol, polyacrylamide, sodium polyacrylate, polyethylene glycol, polyvinyl alcohol, polymaleic anhydride, polyethyleneimine, polyethylene oxide, polyvinyl chloride, starch, water-soluble natural rubber, methyl cellulose, hydroxyethyl cellulose or sodium carboxymethyl cellulose.

[0013] In the preparation method of the hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material, the ratio of the mixed dispersion in step (2) is 0.2:1-2:1 of water-soluble resin solid content: CNF solid content, and the mixing method is magnetic stirring for 2-4 hours.

[0014] In the method for preparing the hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material, the gel prepared in step (2) has a water content of 75%-90%, an aging time of 6-12 hours, and an aging temperature of 65-80°C.

[0015] In the method for preparing the hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material, the pre-curing temperature of the tubular furnace in step (3) is 200-300° C., and the pre-curing time is 1-3 hours.

[0016] In the preparation method of the hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material, in step (3), the temperature is raised after pre-curing to perform carbonization treatment, the carbonization temperature is 500-1000° C., and the carbonization time is 2-4 hours.

[0017] The hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material is prepared by the above method.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The carbon aerogel prepared by the method of the present invention has a volume shrinkage rate of 20%-30% compared to the wet gel, a porosity of 80%-95%, a first-level pore structure size of 1-5 μm, and a second-level pore structure size of 20-500 nm; it has hierarchical porosity, which can effectively improve the specific capacitance of the carbon aerogel compared to the carbon aerogel with a single pore structure.

[0020] 2. The method of the present invention effectively improves the existing preparation process of constructing hierarchical porous structures through an activation step by constructing hierarchical porous structures through in-situ construction.

[0021] 3. The method of the present invention proposes a new idea for preparing carbon aerogels by one-step carbonization of wet gels. The shrinkage rate is controlled based on the dual curing effect of high-strength wet gels cured by catalysts and further enhanced strength by thermal curing. This method skips the traditional dry gel preparation steps of carbon aerogels, effectively shortens the preparation process of carbon aerogels, reduces preparation time, and reduces preparation costs.

[0022] 4. The solvent used in the present invention has low cost and meets actual production needs.

[0023] 5. The method of the present invention is carried out on the basis of existing equipment and does not require any additional equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The apparent morphology of the nanocellulose (CNF) / phenolic resin double network gel in Examples 1, 2, and 3;

[0025] Figure 2 is a microscopic photograph of the hierarchical pore structure of the carbon aerogel in Example 1;

[0026] Figure 3 The compressive strength test results of the wet gels obtained in Examples 1, 2, and 3 are shown;

[0027] Figure 4 The carbon aerogels obtained in Examples 4, 5, and 6 and the volume shrinkage before and after carbonization are shown in FIG.

[0028] Figure 5 1 is the Raman spectrum of the carbonization results of the carbon aerogels obtained in Example 4, Example 5, and Example 6;

[0029] Figure 6 This is a characterization diagram of the electrochemical performance (cyclic voltammetry and constant current charge and discharge) of the carbon aerogel obtained in Example 6. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to specific embodiments.

[0031] Example 1

[0032] A method for preparing a hierarchical porous carbon aerogel fiber-based supercapacitor electrode material comprises the following steps:

[0033] (1) Weigh 30 g of pulp and place it in a blender. Add deionized water and disperse it evenly. Then pour it into a beaker, continue to add deionized water, TEMPO catalyst and sodium bromide, stir evenly, then slowly add NaClO solution, stir at room temperature, and adjust the pH value of the entire reaction system with NaOH solution to keep it stable at 10 until the reaction is completed; filter the reaction solution with a sand core funnel and wash it with a large amount of deionized water until it is neutral to obtain TEMPO-oxidized cellulose; finally, prepare a TEMPO-oxidized cellulose suspension with a concentration of 1 wt%, pour it into a high-pressure homogenizer and circulate homogenize it at a pressure of 100 MPa to obtain a CNF dispersion (2.5 wt%);

[0034] (2) The CNF dispersion was mixed with a water-soluble phenolic resin having a solid content of 25% by weight and uniformly dispersed. Sulfuric acid was used as a curing agent, and a sulfuric acid solution and deionized water having a solid content of 100% of the phenolic resin were prepared. The sulfuric acid solution and deionized water were slowly added dropwise in sequence while magnetic stirring was applied. After the addition was completed, the gel was allowed to stand; the wet gel was placed in an oven at 65°C and dried at normal pressure for 6 hours to obtain an aged wet gel;

[0035] (3) The wet gel sample obtained in step (2) was placed in a tubular furnace for pre-curing at 300°C for 2 h and carbonized at 800°C for 2 h to obtain a hierarchical porous carbon aerogel material, which was recorded as CP1.

[0036] Example 2

[0037] The difference from the above-mentioned Example 1 is that the addition amount of water-soluble phenolic resin is increased to 50% of the CNF solid content, and the other steps remain unchanged. The obtained gel material (denoted as CP2) has improved strength compared with Example 1.

[0038] Example 3

[0039] The difference from the above-mentioned Example 1 is that the addition amount of water-soluble phenolic resin is increased to 100% of the CNF solid content, and the other steps remain unchanged. The obtained gel material (denoted as CP3) has improved strength and significantly reduced porosity compared with Example 1.

[0040] Figure 1 The apparent morphology of the nanocellulose (CNF) / phenolic resin double network gel in Examples 1, 2, and 3 is shown in FIG. Figure 1 It can be seen that the double network gel material was successfully prepared in the above embodiment.

[0041] Figure 2 This is a microscopic photograph of the hierarchical pore structure of the carbon aerogel in Example 1. Figure 2It is shown that carbon aerogel has a rich hierarchical pore structure, which includes macropores larger than 1 μm and small pores smaller than 100 nm. Figure 2 The successful preparation of hierarchical porosity is demonstrated.

[0042] Figure 3 The compressive strength test results of the wet gels obtained in Examples 1, 2, and 3 show that the strength of the gels increases with the addition of phenolic resin, and the gels all have relatively high strength.

[0043] Example 4

[0044] A method for preparing a hierarchical porous carbon aerogel fiber-based supercapacitor electrode material comprises the following steps:

[0045] (1) Weigh 30 g of pulp and place it in a blender. Add deionized water and disperse it evenly. Then pour it into a beaker, continue to add deionized water, TEMPO catalyst and sodium bromide, stir evenly, then slowly add NaClO solution, stir at room temperature, and adjust the pH value of the entire reaction system with NaOH solution to keep it stable at 10 until the reaction is completed; filter the reaction solution with a sand core funnel and wash it with a large amount of deionized water until it is neutral to obtain TEMPO-oxidized cellulose; finally, prepare a TEMPO-oxidized cellulose suspension with a concentration of 1 wt%, pour it into a high-pressure homogenizer and circulate homogenize it at a pressure of 100 MPa to obtain a CNF dispersion (2.5 wt%);

[0046] (2) The CNF dispersion was mixed with a water-soluble phenolic resin having a solid content of 50% by weight and uniformly dispersed. Sulfuric acid was used as a curing agent, and a sulfuric acid solution and deionized water were prepared to have a solid content of 100% of the phenolic resin. The sulfuric acid solution and deionized water were slowly added dropwise while magnetic stirring was applied. After the addition was completed, the gel was allowed to stand. The wet gel was dried in an oven at 65°C at normal pressure for 6 hours to obtain an aged wet gel.

[0047] (3) The wet gel sample obtained in step (2) was placed in a tubular furnace and pre-cured at 300° C. for 2 h to obtain a hierarchical porous carbon aerogel material.

[0048] Example 5

[0049] The difference from the above-mentioned Example 4 is that in addition to pre-curing, a carbonization step is added, the carbonization temperature is 500° C., and the carbonization time is 2 h. The carbonization degree of the obtained gel material is significantly improved compared with Example 4.

[0050] Example 6

[0051] The difference from the above-mentioned Example 4 is that in addition to pre-curing, a carbonization step is added, the carbonization temperature is 800° C., and the carbonization time is 2 h. The carbonization degree of the obtained gel material is significantly improved compared with Examples 4 and 5.

[0052] Figure 4 The carbon aerogels obtained in Examples 4, 5, and 6 are shown, along with photos of their volume shrinkage before and after carbonization. Calculated from the dimensional changes before and after carbonization, the shrinkage of the carbon aerogels was only 26%.

[0053] Figure 5 3 are Raman spectra of the carbonization results of the carbon aerogels obtained in Example 4, Example 5, and Example 6. The results show that the carbon aerogels obtained at 800° C. have the largest ID / IG value and the highest degree of carbonization.

[0054] Figure 6 The electrochemical properties (cyclic voltammetry and constant current charge and discharge) of the carbon aerogel obtained in Example 6 were characterized, and the results showed that the specific capacitance of the carbon aerogel was 148.5 F / g.

[0055] In summary, the preparation method of the present invention not only allows for the in-situ construction of a hierarchical porous carbon aerogel structure, but also reduces the porosity shrinkage during gel drying by improving the gel network strength, thereby shortening the carbon aerogel preparation process through a one-step carbonization method. The hierarchical porous carbon aerogel prepared by the present invention can be used as a supercapacitor electrode material, exhibiting properties such as high strength, high cycle stability, and high specific capacitance. These properties are achieved by producing a hierarchical porous structure using the process parameters of the present invention.

[0056] The preparation method of the present invention has readily available raw materials, low equipment cost, simple operation, and short time consumption, and is very suitable for promotion of industrial production.

Claims

1. A method for preparing a hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material, characterized in that: The carbon aerogel electrode material is obtained by pre-curing and carbonizing the nanofiber filament CNF / water-soluble resin wet gel in a tube furnace in one step; the process comprises the following steps: (1) CNF dispersion was prepared by TEMPO oxidation method; (2) The dispersion prepared in step (1) is mixed and dispersed with the water-soluble resin solution, and a curing agent solution and deionized water in equal proportions to the water-soluble resin are prepared, and the solution is slowly dripped into the stirred solution. After continuous stirring, the solution is allowed to stand and gelled, and the solution is aged in an oven to obtain a high-strength wet gel network; the wet gel has a moisture content of 75%-90%, an aging time of 6-12 h, and an aging temperature of 65-80 °C; The water-soluble resin and the corresponding curing agent are specifically: when the water-soluble resin is a water-soluble phenolic resin, the corresponding curing agent is sulfuric acid; (3) The wet gel sample obtained in step (2) is placed in a tubular furnace for pre-curing to obtain a graded porous carbon aerogel; the pre-curing temperature is 200-300 °C, and the pre-curing time is 1-3 h; after the pre-curing is completed, carbonization treatment is performed, the carbonization temperature is 500-1000 °C, and the carbonization time is 2-4 h.

2. The method for preparing the hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material according to claim 1, characterized in that: The preparation method of the CNF dispersion in step (1) includes: first weighing the wooden raw material and placing it in a blender, adding deionized water to disperse it evenly, then pouring it into a beaker, continuing to add deionized water, TEMPO catalyst and sodium bromide, stirring evenly, slowly adding NaClO solution, stirring at room temperature, and adjusting the pH value of the entire reaction system with NaOH solution to stabilize it at 9.5-10.5 until the reaction is completed; filtering the reaction liquid with a sand core funnel and washing it with a large amount of deionized water until it is neutral to obtain TEMPO-oxidized cellulose; finally, preparing a TEMPO-oxidized cellulose suspension, pouring it into a high-pressure homogenizer and circulating homogenizing it at a pressure of 100 MPa to obtain a CNF dispersion; the concentration of the TEMPO-oxidized cellulose suspension is 0.5 wt%-1 wt%, and the concentration of the CNF dispersion is 2 wt%-3 wt%.

3. The method for preparing the hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material according to claim 1, characterized in that: The ratio of the mixed dispersion in step (2) is 0.2:1-2:1 of water-soluble resin solid content and CNF solid content, and the mixing method is magnetic stirring for 2-4 h.

4. The hierarchical porous cellulose-based carbon aerogel supercapacitor electrode material obtained by the method of claim 1.

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