Conductive carbon material for cement-based electrode, preparation method of conductive carbon material, cement-based electrode and supercapacitor

Abstract

The invention provides a conductive carbon material for a cement-based electrode, a preparation method of the conductive carbon material, the cement-based electrode and a supercapacitor, and relates to the technical field of supercapacitors. The carbon black material with specific pore size distribution is prepared through the chlorination reaction, the specific surface area loss is reduced through surface modification, and the network connectivity of the carbon black is further improved. And the organic electrolyte is used, so that the voltage window is greatly improved, and the capacitance is qualitatively leap.

Description

Technical Field

[0001] The present invention relates to the technical field of cement-based supercapacitors, and particularly to a conductive carbon material for a cement-based electrode, a preparation method thereof, a cement-based electrode, and a supercapacitor. Background Art

[0002] A cement-based electrode is a new type of electrode material prepared from cement, conductive carbon black, etc. Currently, supercapacitors with carbon-cement as electrodes have emerged. However, the conductivity and double-layer capacitance of using conductive carbon black still need to be improved. In current research, the main means to improve the conductivity of carbon-cement electrodes is to increase the dosage of active substances (carbon black) or use the method of extrusion molding to greatly improve the connectivity of the carbon network inside the carbon-cement electrode; regarding the double-layer storage performance of carbon-cement supercapacitors, it has a decisive relationship with the available specific surface area of the electrode composite material. Due to the continuous progress of the cement hydration reaction, the surface of the carbon black is covered by insulating hydration products, seriously reducing the available specific surface area. In addition, the efficient improvement of the double-layer capacitance is highly correlated with the pore size distribution inside the electrode composite material. Pores with a diameter of <200 nm can provide an excellent place for double-layer storage and exhibit a very high specific surface area. Summary of the Invention

[0003] To solve the above problems, the present invention proposes to prepare a carbon black material with a specific pore size distribution through a chlorination reaction, and through surface modification, reduce the loss of the specific surface area of the electrode material and further improve the connectivity of the carbon black network. Using an organic electrolyte greatly improves the voltage window, resulting in a qualitative leap in its capacitance.

[0004] One of the purposes of the present invention is to provide a preparation method of a conductive carbon material for a cement-based electrode.

[0005] Another purpose of the present invention is to provide a conductive carbon material for a cement-based electrode prepared by this preparation method.

[0006] A third purpose of the present invention is to provide a cement-based electrode prepared from this conductive carbon material.

[0007] A fourth purpose of the present invention is to provide a supercapacitor including this cement-based electrode.

[0008] In order to achieve the above purposes of the present invention, the following technical solutions are specifically adopted:

[0009] In the first aspect, the present invention provides a preparation method of a conductive carbon material for a cement-based electrode, including the following steps:

[0010] 1) Load the silicon carbide powder into a quartz reaction tube and place it in a high-temperature furnace. First, introduce an inert gas to remove air, heat up the high-temperature furnace, and then introduce chlorine for chlorination reaction. After the reaction is completed, stop the supply of chlorine and continue to introduce the inert gas to cool the reaction tube to room temperature to obtain carbide-derived carbon. The temperature of the chlorination reaction is 800 - 1000 °C, and the time is 2 - 6 h;

[0011] 2) Surface-modify the carbide-derived carbon obtained in step 1) with a silane coupling agent to obtain a conductive carbon material for a cement-based electrode.

[0012] The following is a detailed description of each step:

[0013] Step 1):

[0014] Load the silicon carbide powder into the quartz reaction tube and spread it as evenly as possible to avoid accumulation. Install the reaction tube loaded with the silicon carbide powder in the high-temperature furnace and ensure that the inlets and outlets of chlorine and the inert gas are well connected.

[0015] Before starting the chlorination reaction, first introduce an inert gas (such as argon) to remove the air in the reaction tube and prevent oxidation reactions.

[0016] Preferably, the flow rate of the inert gas is 100 - 200 ml / min, preferably 150 ml / min, and the gas is continuously introduced for 15 - 45 minutes, preferably about 30 minutes.

[0017] While introducing the inert gas, heat up the high-temperature furnace to 800 - 1000 °C, preferably 900 °C (the chlorination reaction temperature).

[0018] When the temperature reaches the set value, gradually introduce chlorine while maintaining the flow of the inert gas.

[0019] Preferably, the flow rate of chlorine is 50 - 200 ml / min, preferably 50 ml / min.

[0020] Chlorine reacts with silicon carbide to form silicon tetrachloride (SiCl4) and leave the reaction tube, and the remaining carbon forms a porous structure. After the reaction is completed, stop the supply of chlorine and continue to introduce the inert gas to cool the reaction tube to room temperature.

[0021] By regulating the temperature, flow rate, and reaction time of the high-temperature chlorination reaction of silicon carbide, etc., the size of the micropores is changed to achieve precise control of the pore structure distribution.

[0022] In the carbide-derived carbon obtained in step 1), the pore volume of pores smaller than 200 nm accounts for more than 70% of the total pore volume, and the pore volume of pores smaller than 900 nm accounts for more than 90% of the total pore volume; the specific surface area of the carbide-derived carbon is 1450 - 1800 m 2 / g.

[0023] It should be noted that the pore volume ratio of pores smaller than 200 nm is the pore volume of all pores smaller than 200 nm statistically by BET divided by the total pore volume, and the pore volume ratio of pores smaller than 900 nm is the pore volume of all pores smaller than 900 nm statistically by BET divided by the total pore volume.

[0024] Step 2):

[0025] In some embodiments, Step 2) includes:

[0026] a) Cleaning and drying the carbide-derived carbon;

[0027] b) Dissolving the silane coupling agent in anhydrous toluene to obtain a silane coupling agent solution;

[0028] c) Placing the dried carbide-derived carbon in a reaction vessel, adding the silane coupling agent solution for reaction reflux, cooling to room temperature after the reaction, washing and drying to obtain a conductive carbon material for a cement-based electrode.

[0029] Step a):

[0030] Ultrasonically clean the carbide-derived carbon with deionized water and ethanol to remove surface impurities. Dry the sample in a vacuum drying oven to ensure that the sample is completely dry to prevent moisture from affecting subsequent surface modification.

[0031] Step b):

[0032] Preferably, the silane coupling agent is trichloromethylsilane.

[0033] Step c):

[0034] Place the carbide-derived carbon in a reaction vessel and add the prepared silane coupling agent solution. Install a condensing reflux device to prevent solvent volatilization.

[0035] Preferably, the dosage of the silane coupling agent is 2%-10% of the mass of the carbide-derived carbon, preferably 8%.

[0036] Preferably, the reaction reflux temperature is 80-110 °C and the time is 24 hours.

[0037] After the reaction, cool the reaction vessel to room temperature, wash the sample with anhydrous toluene to remove the unreacted silane coupling agent; wash the modified porous carbon with anhydrous ethanol multiple times to remove the residual reactants; finally wash with deionized water to ensure complete removal of the solvent and unreacted substances. Dry the washed sample in a vacuum drying oven to ensure that the sample is completely dry.

[0038] The surface of carbide-derived carbon is modified by long-chain alkyl groups, aiming to reduce the influence of the formation of hydration products on the pore structure in the subsequent preparation of cement-based materials, so as to form a cement-based electrode material with a super high specific surface area.

[0039] In a second aspect, the present invention provides a conductive carbon material for a cement-based electrode prepared by the above preparation method.

[0040] In the conductive carbon material, the pore volume of pores smaller than 200 nm accounts for more than 70% of the total pore volume, and the pore volume of pores smaller than 900 nm accounts for more than 90% of the total pore volume; the specific surface area of the carbide-derived carbon is 1450 - 1800 m 2 / g.

[0041] The present invention controls the pore structure of the prepared carbide-derived carbon to improve the conductivity by using a specific carbide to carry out a chlorination reaction under specific conditions, and modifies the surface with hydrophobic functional groups to reduce the problem that the hydration products of cement mixing cover the carbon material during the preparation of the cement-based electrode, resulting in pore blockage and affecting the electrical performance.

[0042] In a third aspect, the present invention provides a cement-based electrode prepared from the above conductive carbon material for a cement-based electrode and cement.

[0043] In some embodiments, the cement-based electrode is prepared by the following method:

[0044] Mix the conductive carbon material and cement to obtain a dry mixture, add water and a water reducing agent and mix and stir to obtain a cement-based slurry; pour the cement-based slurry into a mold, vibrate it, demold, cure, cut, and polish it after hardening to obtain a cement-based electrode.

[0045] Preferably, the cement is one or more selected from Portland cement, ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, fly ash Portland cement, composite Portland cement, medium heat Portland cement, low heat slag Portland cement, and white Portland cement. The cement strength grade can be 425, 625, 325, 525, etc., without special limitation;

[0046] Preferably, the mass of the conductive carbon material accounts for 8% - 13% of the mass of the cement;

[0047] Preferably, the water reducing agent is one or more selected from polycarboxylate superplasticizer and naphthalene superplasticizer;

[0048] Preferably, the water-cement ratio is 0.8 - 1.6, and the mass of the water reducing agent accounts for 2% - 4% of the mass of the water.

[0049] Preferably, the curing temperature is 20 ± 2 °C, the relative humidity is controlled above 95%, and the curing is carried out for more than 28 days.

[0050] The specific surface area of the obtained cement-based electrode is 300-500 m 2 / g.

[0051] Fourthly, the present invention provides a supercapacitor, including the above-mentioned cement-based electrode;

[0052] The cement-based electrode is soaked in an organic electrolyte until saturated, and the supercapacitor is encapsulated according to the cement-based electrode, glass fiber membrane, and cement-based electrode.

[0053] Beneficial effects:

[0054] The conductive carbon material of the present invention relies on an ultra-high specific surface area, which can greatly improve the storage efficiency of the electric double layer. Through precise control of the pore structure distribution, the efficiency of the electric double layer can be maximized. The tiny pores inside the cement-based conductive material, as the main contributing part of the specific surface area, also provide a large number of adsorption sites for charge storage. The medium and large pores serve as fast channels for ion transport and excellent sites for electrolyte storage.

[0055] The present invention has been described in detail above, but the above embodiments are essentially illustrative only and are not intended to limit the present invention. In addition, the present invention is not limited by any theory described in the foregoing prior art or the invention content or the following embodiments. Description of the drawings

[0056] Figure 1 Shows the SEM image of the conductive carbon material prepared in Example 1;

[0057] Figure 2 Shows the pore size distribution curve of the conductive carbon material prepared in Example 1;

[0058] Figure 3 Shows the adsorption and desorption curve of the conductive carbon material prepared in Example 1;

[0059] Figure 4 Shows the resistance-pressure curve of the cement-based electrode material prepared in Example 1. Specific embodiments

[0060] The following further illustrates the present invention with reference to embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection required by the present invention.

[0061] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the embodiments are all conventional raw materials, reagents, methods in the art.

[0062] The materials and equipment used in the embodiments are as follows:

[0063] β-SiC powder comes from Angxing New Carbon Materials Changzhou Co., Ltd.;

[0064] High-purity chlorine gas (>99.9%) is from Shandong Yanhe Chemical Co., Ltd.;

[0065] Trichloromethylsilane is from Shanghai Macklin Biochemical Co., Ltd.

[0066] Example 1

[0067] Preparation of cement-based conductive carbon material:

[0068] Take 25 g of high-purity β-SiC and evenly distribute it in a quartz reaction tube to avoid accumulation. Place the reaction tube loaded with silicon carbide powder into a high-temperature furnace, ensuring that the inlets and outlets of chlorine gas and inert gas are well connected. Pass argon at 150 ml / min to purge the air in the reaction tube and prevent oxidation reaction, and continue to pass the gas for about 30 minutes.

[0069] While passing the inert gas, heat the high-temperature furnace to 900 °C, gradually introduce high-purity chlorine gas (>99.9%), control the flow rate of chlorine gas at 50 ml / min, and the reaction time is 2.5 hours.

[0070] After the reaction is completed, stop the supply of chlorine gas, continue to pass the inert gas, and cool the reaction tube to room temperature.

[0071] Let the prepared carbide derivative (about 10.4 g) stand for 24 h, then ultrasonically clean it with deionized water and ethanol to remove surface impurities.

[0072] Dissolve 0.5 g of trichloromethylsilane in 100 g of anhydrous toluene to obtain a trichloromethylsilane solution. Place the above carbide derivative sample in a reaction vessel, add the prepared trichloromethylsilane solution, control the reaction temperature at 110 °C, and the time is 24 hours.

[0073] Cool the reaction vessel to room temperature, wash the sample with anhydrous toluene to remove the unreacted silane coupling agent. Wash the modified carbon porous structure sample with anhydrous ethanol multiple times to remove the residual reactants. Finally, wash it with deionized water to ensure that the solvent and unreacted substances are completely removed. Dry the washed sample in a vacuum drying oven to ensure that the sample is completely dry, and obtain the cement-based conductive carbon material.

[0074] Use SEM to observe the morphology of the cement-based conductive carbon material. The results are as Figure 1 shown. It can be seen that there are dispersed particulate substances in the material, which are carbon black particles or cement hydration products. The accumulation between the particles may provide the conduction paths for electrons and ions. Some regions in the image show sheet-like or layered structures (such as the local area on the right), which are the characteristics of carbon black aggregates. Use BET nitrogen adsorption to measure the specific surface area. The results are as Figure 2 shown. The specific surface area of the conductive carbon material is 1742.41 m2 / g. The adsorption and desorption curves of the conductive carbon material were tested using nitrogen adsorption, and the results are as Figure 3 shown. It can be seen that this adsorption and desorption behavior indicates that the material has a high specific surface area and a suitable pore structure (combination of micropores and mesopores), which is very beneficial for supercapacitor electrode materials and can improve the ion storage capacity and rapid transmission capacity.

[0075] Preparation of cement-based electrode material:

[0076] Finally, the modified porous carbon (cement-based conductive carbon material) was mixed with 100 g of dry Portland cement powder at a mass ratio of 8%, with a water-cement ratio of 1.35. The mass of the water-reducing agent (Qingdao Huatie polycarboxylate superplasticizer HT-300) was 2% of the mass of water, and water was added for mixing. The above mixture was stirred for 20 min until it was evenly mixed. It was poured into a mold of 10 cm * 10 cm * 10 cm and placed on a vibrating table for vibration for 10 min. After hardening, it was demolded and placed in a curing box at a temperature of 20 ± 2 °C and a relative humidity controlled above 95% for 28 days.

[0077] The specific surface area of the cement-based electrode material was measured using BET nitrogen adsorption, and the results are shown in Table 1.

[0078] The resistance of the cement-based electrode material was measured using the four-probe method, and the results are as Figure 4 shown. The resistance of the electrode material decreased significantly under pressure, indicating that its conductivity was relatively ideal.

[0079] Preparation of supercapacitor:

[0080] Organic electrolyte: 0.94 g of LiPF 6 was added to 10 mL of propylene carbonate. It was stirred using a magnetic stirrer until the electrolyte was completely dissolved. Usually, the dissolution time was 30 minutes to 1 hour. The prepared electrolyte was filtered using a 0.2-μm syringe filter to remove possible solid impurities and undissolved particles. The filtered electrolyte should be stored in an anhydrous environment to avoid contact with moisture in the air.

[0081] The cement-based electrode material was immersed in 1 M organic electrolyte until saturated, and a supercapacitor was assembled in the order of cement-based electrode material, glass fiber membrane, and cement-based electrode material.

[0082] The specific capacitance is the capacitance value / the mass of two electrode plates. Through cyclic voltammetry (CV), the scanning voltage range: was set to -2 V to 2 V, and for aqueous electrolyte it was -1 V to 1 V.

[0083] Scanning rate: was set to 100 mV / s, and multiple scanning rates were tested to evaluate the effect of the rate on the performance.

[0084] Specific capacitance: The specific capacitance is used to define the electricity storage performance. Using the CHI760E electrochemical workstation, the specific capacitance calculation formula where C is the specific capacitance, I is the test current, ΔV is the voltage gradient, u is the scanning rate, U 0 is the voltage window difference, and m is the mass of the active material (carbon black) used.

[0085] The results are shown in Table 1.

[0086] Example 2

[0087] The preparation process is basically the same as that of Example 1, except that: the reaction time of the chlorination reaction is set to 6 hours. Tested according to the method of Example 1, the results are shown in Table 1.

[0088] Example 3

[0089] The preparation process is basically the same as that of Example 1, except that: the temperature of the chlorination reaction is set to 1000 °C. Tested according to the method of Example 1, the results are shown in Table 1.

[0090] Comparative Example 1

[0091] No surface modification operation is carried out, and other steps are the same as those of Example 1. Tested according to the method of Example 1, the results are shown in Table 1.

[0092] Comparative Example 2

[0093] The temperature of the chlorination reaction is set to 1200 °C, and other steps are the same as those of Example 1. Tested according to the method of Example 1, the results are shown in Table 1.

[0094] Comparative Example 3

[0095] Use 1M potassium chloride solution as the electrolyte, and other steps are the same as those of Example 1. Tested according to the method of Example 1, the results are shown in Table 1.

[0096] Table 1

[0097]

[0098] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: within the scope of the spirit and essence defined by the claims of the present invention, the technical solutions described in the foregoing embodiments can be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A method for preparing a conductive carbon material for a cement-based electrode, characterized in that: The following steps are involved: 1) Put silicon carbide powder into a quartz reaction tube and put it into a high-temperature furnace, first introduce inert gas to exclude air, heat the high-temperature furnace, and then introduce chlorine gas for chlorination reaction. After the reaction is completed, stop the chlorine supply, continue to introduce inert gas, cool the reaction tube to room temperature, and obtain carbide-derived carbon; wherein the temperature of the chlorination reaction is 800-1000° C., and the time is 2-6 hours; 2) The carbide-derived carbon obtained in step 1) is surface-modified with a silane coupling agent to obtain a conductive carbon material for cement-based electrodes.

2. The preparation method according to claim 1, characterized in that: In step 1), the flow rate of the inert gas is 100-200 ml / min, and the ventilation is continued for 15-45 minutes.

3. The preparation method according to claim 1, characterized in that: In step 1), the flow rate of chlorine gas is 50-200 ml / min.

4. The preparation method according to claim 1, characterized in that: In the carbide-derived carbon obtained in step 1), the pore volume of pores smaller than 200 nm accounts for more than 70% of the total pore volume, and the pore volume of pores smaller than 900 nm accounts for more than 90% of the total pore volume; the specific surface area of ​​the carbide-derived carbon is 1450-1800m 2 / g.

5. The preparation method according to claim 1, characterized in that: Step 2) includes: a) washing and drying the carbide-derived carbon; b) dissolving the silane coupling agent in anhydrous toluene to obtain a silane coupling agent solution; c) placing the dried carbide-derived carbon in a reaction container, adding a silane coupling agent solution for reaction reflux, cooling to room temperature after the reaction, washing and drying to obtain a conductive carbon material for cement-based electrodes.

6. The preparation method according to claim 5, characterized in that: The silane coupling agent in step b) is trichloromethylsilane; The amount of the silane coupling agent in step c) is 2%-10% of the mass of the carbide-derived carbon; The reaction reflux temperature of step c) is 80-110° C. and the reaction time is 24 hours.

7. A conductive carbon material for cement-based electrodes, characterized in that: Prepared by the preparation method according to any one of claims 1 to 6; The pore volume of pores smaller than 200nm in the conductive carbon material accounts for more than 70% of the total pore volume, and the pore volume of pores smaller than 900nm accounts for more than 90% of the total pore volume; the specific surface area of ​​carbide-derived carbon is 1450-1800m 2 / g.

8. A cement-based electrode, characterized in that: The conductive carbon material for cement-based electrodes according to claim 7 is prepared by using cement.

9. The cement-based electrode according to claim 8, characterized in that: The cement-based electrode was prepared by the following method: The conductive carbon material and cement are mixed to obtain a dry mixture, and water and a water reducing agent are added and mixed to obtain a cement-based slurry; the cement-based slurry is poured into a mold and vibrated, and after hardening, the slurry is demoulded, cured, cut, and polished to obtain a cement-based electrode; The specific surface area of ​​cement-based electrodes is 300-500m 2 / g.

10. A supercapacitor, characterized in that: The supercapacitor comprises the cement-based electrode according to claim 8 or 9; The cement-based electrode is immersed in an organic electrolyte until saturated, and the cement-based electrode, the glass fiber membrane, and the cement-based electrode are packaged into a supercapacitor.

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