Preparation method of carbon quantum dot MXene composite material

Abstract

The application discloses a preparation method of a carbon quantum dot MXene composite material, and belongs to the field of capacitive materials. The preparation method comprises the following steps: preparing eicosanoic acid modified carbon quantum dots, carrying out MXene intercalation modification, and preparing a composite material by using a spin coating method. When the composite material prepared by the method is used as a capacitive material, the cyclic stability is good, and a high capacitance can be maintained after multiple cycles, and the capacitance retention rate after 20000 cycles is 93.3%-94.1%.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a carbon quantum dot MXene composite material and belongs to the field of capacitive materials. BACKGROUND

[0002] As a new type of energy storage device, supercapacitors have shown great application potential in the fields of portable electronic devices, electric vehicles, smart grids, aerospace, etc. due to their fast charge and discharge speed, high power density, long cycle life and other remarkable advantages.

[0003] Although supercapacitors have many advantages, their energy density is relatively low (usually less than 30 Wh kg-1) at present, which largely limits their further promotion in long-lasting applications. Therefore, developing high-performance supercapacitor electrode materials to improve their energy density has become a research hotspot and key breakthrough direction in the current energy storage field.

[0004] In recent years, two-dimensional transition metal carbides / nitrides (MXenes) have gradually become the focus of research on supercapacitor electrode materials due to their unique physical and chemical properties. MXenes materials have high electrical conductivity, rich surface functional groups and adjustable layered structure, which make them show great potential in the field of energy storage.

[0005] However, MXene nanosheets also face some challenges in practical applications. Due to the action of van der Waals force, MXene nanosheets are prone to stacking, which significantly reduces their specific surface area and electrochemical active sites, thereby limiting the development of their electrochemical performance. Taking Ti3C2Tx as an example, its interlayer spacing is small, and electrolyte ions are difficult to fully enter the interlayer, which not only reduces the specific surface area of the material, but also reduces the available electrochemical active sites. In addition, MXene also has the problem of self-oxidation. When in contact with air or moisture, the titanium atoms on the surface are easy to react with oxygen or water to generate non-conductive TiO2, which further reduces the electronic conductivity and capacitive active sites of the material, affecting its long-term stability and practical application.

[0006] Carbon quantum dots (CQDs) are a class of zero-dimensional carbon-based nanomaterials with a size of less than 10 nanometers, which are composed of carbon atoms and their surface functional groups (such as -COOH, -OH, etc.), and have fluorescence properties, good water solubility and biocompatibility. Studies have shown that carbon quantum dots can passivate the edges of MXene to delay its oxidation, mainly through chemical modification and physical barrier effect of its surface functional groups, which can maintain a high capacitance retention rate in a humid environment. In addition, carbon quantum dots can also inhibit the stacking of MXene, increase its specific surface area and electrochemically active sites. The emergence of carbon quantum dot (CQDs) and MXene composite material is the result of the cross-fusion of two-dimensional material science, nanotechnology and energy science.

[0007] However, in practical applications, although the intercalation of CQDs can inhibit the stacking of MXene, increase its specific surface area and electrochemically active sites, and improve its capacitance, the energy density under high power density will decrease significantly, especially when used as a component of an asymmetric capacitor. In addition, its cycle stability is poor, and the capacitance will decrease significantly after a large number of cycles. SUMMARY

[0008] The technical problem to be solved by the present application is to overcome the defects of the prior art. By using eicosanoic acid to modify carbon quantum dots and intercalate MXene, a composite material is finally prepared by a spin coating method, so as to improve the capacitance of the material when used as a capacitor material, reduce the energy density loss under high power density, and improve the cycle stability of the material.

[0009] To solve the above technical problems, the present application adopts the following technical solutions:

[0010] A preparation method of a carbon quantum dot MXene composite material, the preparation method comprising preparing eicosanoic acid modified carbon quantum dots, intercalating MXene, and preparing a composite material by a spin coating method.

[0011] The following is a further improvement on the above technical solution:

[0012] The method for preparing eicosanoic acid modified carbon quantum dots is as follows: lignin carbon quantum dots doped with nitrogen elements are dispersed in anhydrous ethanol, ultrasonic dispersion is performed for 15-25 min, and then the mixture is kept at 60-70℃ for preservation to obtain a carbon quantum dot dispersion liquid for standby use. Eicosanoic acid, 1-cyclohexyl-2-morpholinoethyl carbodiimide p-toluenesulfonate and dichloromethane are uniformly mixed, and then added to the preserved carbon quantum dot dispersion liquid. The temperature is kept at 60-70℃, and stirring is performed for 23-25 h. After stirring, filtration, washing and drying are performed to obtain eicosanoic acid modified carbon quantum dots.

[0013] The mass ratio of the nitrogen element doped lignin carbon quantum dots to anhydrous ethanol is 1:9-11;

[0014] The nitrogen element content of the nitrogen element doped lignin carbon quantum dots is 11.5at%;

[0015] The mass ratio of the heat-preserved carbon quantum dot dispersion liquid, eicosanoic acid, 1-cyclohexyl-2-morpholinoethyl carbodiimide p-toluenesulfonate, dichloromethane is 225-275:1.8-2.2:6.5-7.5:225-275.

[0016] The method for intercalating modification of MXene is to mix MXene with deionized water, perform ultrasonic dispersion, the ultrasonic time is 15-25min, after ultrasonic completion, MXene dispersion liquid is obtained for standby, then sodium stannate, lithium sulfate and deionized water are mixed and stirred, after stirring to complete dissolution, a mixed salt solution is obtained, then the MXene dispersion liquid, the mixed salt solution and urea are mixed, the temperature is controlled to be 115-125℃, hydrothermal reaction is performed, the hydrothermal reaction time is 20-26h, after reaction completion, filtration, washing and drying are performed, and the intercalation modified MXene is obtained;

[0017] The mass ratio of the MXene to deionized water is 1:9-11;

[0018] The size of the MXene is 170nm;

[0019] The mass ratio of the sodium stannate, lithium sulfate and deionized water is 0.9-1.1:1.8-2.2:14-16;

[0020] The mass ratio of the MXene dispersion liquid, the mixed salt solution and urea is 6.5-7.5:13-17:13-17.

[0021] The method for preparing the composite material by the spin coating method is to mix the eicosanoic acid modified carbon quantum dots with deionized water to prepare a carbon quantum dot suspension liquid, mix the intercalation modified MXene with deionized water to prepare an MXene suspension liquid, then mix the carbon quantum dot suspension liquid and the MXene suspension liquid, use ammonia water to adjust the pH to be 8.3-8.7, then add polyethylene glycol octylphenyl ether solution, continue to stir, the stirring time is 10-14h, a composite liquid is obtained, the rotation speed is controlled to be 2500-3500r / min, spin coating is performed, after spin coating completion, the temperature is controlled to be 75-85℃, drying is performed in a vacuum drying box, the drying time is 16-20h, after drying completion, the temperature is controlled to be 375-425℃, annealing is performed under an argon atmosphere, the annealing time is controlled to be 1.5-2.5h, and the carbon quantum dot MXene composite material is obtained after annealing completion;

[0022] The concentration of the eicosanoic acid modified carbon quantum dots in the carbon quantum dot suspension is 1.75-2.25 mg / mL;

[0023] The concentration of the intercalation modified MXene in the MXene suspension is 4.5-5.5 mg / mL;

[0024] The volume ratio of the carbon quantum dot suspension and the MXene suspension is 1:1.5-2.5.

[0025] The added amount of the polyethylene glycol octylphenyl ether solution is 0.075-0.125% of the total volume of the carbon quantum dot suspension and the MXene suspension.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] In the method for preparing eicosanoic acid modified carbon quantum dots, under the coupling action of 1-cyclohexyl-2-morpholinoethyl carbodiimide p-toluenesulfonate, eicosanoic acid and carbon quantum dots undergo condensation, and the surface of the carbon quantum dots is modified to obtain eicosanoic acid modified carbon quantum dots. In the MXene intercalation modification method, tin and lithium elements are intercalated into the interlayer of MXene through the intercalation of urea in a hydrothermal environment. The eicosanoic acid modified carbon quantum dots and the intercalation modified MXene are prepared into a composite material by a spin coating method. Experimental results show that the electrochemical performance of the material can be effectively improved.

[0028] When the prepared composite material is used as a capacitor material, it has high rate performance. Under different scan speeds and different current densities, it can maintain high capacitance. Under a 10 mV / s scan speed, the capacitance is 335-342 F / g; under a 50 mV / s scan speed, the capacitance is 332-335 F / g; under a 100 mV / s scan speed, the capacitance is 309-315 F / g; under a 200 mV / s scan speed, the capacitance is 275-281 F / g; under a 500 mV / s scan speed, the capacitance is 243-245 F / g; under a 1000 mV / s scan speed, the capacitance is 219-224 F / g; under a 2000 mV / s scan speed, the capacitance is 208-210 F / g; under a current density of 1 A / g, the capacitance is 348-353 F / g; under a current density of 5 A / g, the capacitance is 334-339 F / g; under a current density of 10 A / g, the capacitance is 307-310 F / g; under a current density of 50 A / g, the capacitance is 281-288 F / g; under a current density of 100 A / g, the capacitance is 275-279 F / g; under a current density of 500 A / g, the capacitance is 254-261 F / g; and under a current density of 1000 A / g, the capacitance is 204-213 F / g.

[0029] The prepared composite material has good cycle stability when used as a capacitor material, and the capacity retention rate after 2000 cycles is 99.8%-99.9%, the capacity retention rate after 5000 cycles is 98.6%-98.7%, the capacity retention rate after 10000 cycles is 95.8%-96.2%, the capacity retention rate after 15000 cycles is 95.2%-95.5%, and the capacity retention rate after 20000 cycles is 93.3%-94.1%;

[0030] The prepared composite material has high energy density under different power densities when used as a capacitor material, and the energy density is 30.9-31.2Wh / kg when the power density is 1kW / kg, the energy density is 30.1-30.8Wh / kg when the power density is 5kW / kg, the energy density is 28.5-28.8Wh / kg when the power density is 10kW / kg, and the energy density is 25.3-26.1Wh / kg when the power density is 50kW / kg. DETAILED DESCRIPTION Embodiment 1

[0031] (1) Preparation of eicosanoic acid modified carbon quantum dots

[0032] The nitrogen element doped lignin carbon quantum dots are dispersed in anhydrous ethanol, ultrasonic dispersion is carried out, the ultrasonic time is 20min, after ultrasonic completion, the temperature is kept at 65℃, the carbon quantum dot dispersion liquid is obtained and reserved, eicosanoic acid, 1-cyclohexyl-2-morpholinoethyl carbodiimide p-toluenesulfonate and dichloromethane are uniformly mixed, then added to the reserved carbon quantum dot dispersion liquid, the temperature is kept at 65℃, stirring is carried out, the stirring time is 24h, after stirring completion, filtration, washing and drying are carried out, and eicosanoic acid modified carbon quantum dots are obtained.

[0033] The mass ratio of the nitrogen element doped lignin carbon quantum dots to anhydrous ethanol is 1:10;

[0034] The nitrogen element content of the nitrogen element doped lignin carbon quantum dots is 11.5at%;

[0035] The mass ratio of the reserved carbon quantum dot dispersion liquid, eicosanoic acid, 1-cyclohexyl-2-morpholinoethyl carbodiimide p-toluenesulfonate and dichloromethane is 250:2:7:250.

[0036] (2) MXene intercalation modification

[0037] MXene is mixed with deionized water for ultrasonic dispersion, the ultrasonic time is 20 min, and the MXene dispersion liquid is obtained after ultrasonic completion and is ready for use. Then sodium stannate, lithium sulfate and deionized water are mixed and stirred to obtain a mixed salt solution. Then the MXene dispersion liquid, the mixed salt solution and urea are mixed, the temperature is controlled at 120 DEG C, and the hydrothermal reaction is carried out for 24 h. After reaction, filtration, washing and drying are carried out to obtain the intercalated modified MXene.

[0038] The mass ratio of the MXene to deionized water is 1:10.

[0039] The size of the MXene is 170 nm.

[0040] The mass ratio of the sodium stannate, lithium sulfate and deionized water is 1:2:15.

[0041] The mass ratio of the MXene dispersion liquid, the mixed salt solution and urea is 7:15:15.

[0042] (3) Preparation of the composite material by spin coating method

[0043] Eicosanoic acid modified carbon quantum dots are mixed with deionized water to prepare a carbon quantum dot suspension liquid, and the intercalated modified MXene is mixed with deionized water to prepare an MXene suspension liquid. Then the carbon quantum dot suspension liquid and the MXene suspension liquid are mixed, ammonia water is used to adjust the pH to 8.5, and then a polyethylene glycol octylphenyl ether solution is added and stirred for 12 h to obtain a composite liquid. The rotation speed is controlled at 3000 r / min, spin coating is carried out, the temperature is controlled at 80 DEG C after spin coating, and drying is carried out in a vacuum drying oven for 18 h. The temperature is controlled at 400 DEG C after drying, annealing is carried out in an argon atmosphere for 2 h, and the carbon quantum dot MXene composite material is obtained after annealing.

[0044] The concentration of the eicosanoic acid modified carbon quantum dots in the carbon quantum dot suspension liquid is 2 mg / mL.

[0045] The concentration of the intercalated modified MXene in the MXene suspension liquid is 5 mg / mL.

[0046] The volume ratio of the carbon quantum dot suspension liquid to the MXene suspension liquid is 1:2.

[0047] The addition amount of the polyethylene glycol octylphenyl ether solution is 0.1% of the total volume of the carbon quantum dot suspension liquid and the MXene suspension liquid. Example 2

[0048] (1) Preparation of eicosanoic acid modified carbon quantum dots

[0049] The nitrogen element doped lignin carbon quantum dots are dispersed in anhydrous ethanol, ultrasonic dispersion is carried out, the ultrasonic time is 15 min, after ultrasonic completion, preservation is carried out at 60 DEG C, carbon quantum dot dispersion liquid is obtained for standby, eicosanoic acid, 1-cyclohexyl-2-morpholinoethyl carbodiimide p-toluenesulfonate, dichloromethane are uniformly mixed, then added to the preserved carbon quantum dot dispersion liquid, the temperature is kept at 60 DEG C, stirring is carried out, the stirring time is 25 h, after stirring completion, filtration, washing and drying are carried out, eicosanoic acid modified carbon quantum dots are obtained;

[0050] The mass ratio of the nitrogen element doped lignin carbon quantum dots and anhydrous ethanol is 1:9;

[0051] The nitrogen element content of the nitrogen element doped lignin carbon quantum dots is 11.5 at%;

[0052] The mass ratio of the preserved carbon quantum dot dispersion liquid, eicosanoic acid, 1-cyclohexyl-2-morpholinoethyl carbodiimide p-toluenesulfonate and dichloromethane is 225:1.8:6.5:225.

[0053] (2) MXene intercalation modification

[0054] MXene is mixed with deionized water, ultrasonic dispersion is carried out, the ultrasonic time is 15 min, after ultrasonic completion, MXene dispersion liquid is obtained for standby, then sodium stannate, lithium sulfate and deionized water are mixed and stirred, after stirring to complete dissolution, mixed salt solution is obtained, then the MXene dispersion liquid, the mixed salt solution and urea are mixed, the temperature is controlled at 125 DEG C, hydrothermal reaction is carried out, the hydrothermal reaction time is 20 h, after reaction completion, filtration, washing and drying are carried out, intercalation modified MXene is obtained;

[0055] The mass ratio of the MXene and deionized water is 1:9;

[0056] The size of the MXene is 170 nm;

[0057] The mass ratio of the sodium stannate, lithium sulfate and deionized water is 0.9:1.8:14;

[0058] The mass ratio of the MXene dispersion liquid, the mixed salt solution and urea is 6.5:13:13.

[0059] (3) Preparation of composite material by spin coating method

[0060] The eicosanoic acid modified carbon quantum dots are mixed with deionized water to prepare a carbon quantum dot suspension, the intercalation modified MXene is mixed with deionized water to prepare a MXene suspension, then the carbon quantum dot suspension and the MXene suspension are mixed, ammonia water is used to adjust the pH to 8.3, then a polyethylene glycol octylphenyl ether solution is added, and stirring is continued for 14 hours to obtain a composite liquid, the speed is controlled at 2500 r / min, and the composite liquid is spin-coated, the temperature is controlled at 75 DEG C after spin coating, and the composite liquid is dried in a vacuum drying box for 20 hours, the temperature is controlled at 375 DEG C after drying, and the composite liquid is annealed in an argon atmosphere for 1.5 hours to obtain a carbon quantum dot MXene composite material;

[0061] The concentration of the eicosanoic acid modified carbon quantum dots in the carbon quantum dot suspension is 1.75 mg / mL;

[0062] The concentration of the intercalation modified MXene in the MXene suspension is 4.5 mg / mL;

[0063] The volume ratio of the carbon quantum dot suspension and the MXene suspension is 1:1.5.

[0064] The addition amount of the polyethylene glycol octylphenyl ether solution is 0.075% of the total volume of the carbon quantum dot suspension and the MXene suspension. Example 3

[0065] (1) Preparation of eicosanoic acid modified carbon quantum dots

[0066] The nitrogen element doped lignin carbon quantum dots are dispersed in anhydrous ethanol and ultrasonically dispersed for 25 minutes, and then incubated at 70 DEG C to obtain a carbon quantum dot dispersion liquid for standby, eicosanoic acid, 1-cyclohexyl-2-morpholinoethyl carbodiimide p-toluenesulfonate and dichloromethane are uniformly mixed and then added to the incubated carbon quantum dot dispersion liquid, the temperature is maintained at 70 DEG C, and stirring is performed for 23 hours, after which the eicosanoic acid modified carbon quantum dots are obtained by filtration, washing and drying;

[0067] The mass ratio of the nitrogen element doped lignin carbon quantum dots and anhydrous ethanol is 1:11;

[0068] The nitrogen element content of the nitrogen element doped lignin carbon quantum dots is 11.5 at%;

[0069] The mass ratio of the incubated carbon quantum dot dispersion liquid, eicosanoic acid, 1-cyclohexyl-2-morpholinoethyl carbodiimide p-toluenesulfonate and dichloromethane is 275:2.2:7.5:275.

[0070] (2) MXene intercalation modification

[0071] MXene is mixed with deionized water for ultrasonic dispersion, the ultrasonic time is 25 min, and the MXene dispersion liquid is obtained after ultrasonic completion for standby. Then sodium stannate, lithium sulfate and deionized water are mixed and stirred to obtain a mixed salt solution. Then the MXene dispersion liquid, the mixed salt solution and urea are mixed, the temperature is controlled at 115 DEG C, and the hydrothermal reaction is carried out for 26 h. After the reaction is completed, the intercalation modified MXene is obtained by filtration, washing and drying.

[0072] The mass ratio of the MXene to deionized water is 1:11;

[0073] The size of the MXene is 170 nm;

[0074] The mass ratio of the sodium stannate, lithium sulfate and deionized water is 1.1:2.2:16;

[0075] The mass ratio of the MXene dispersion liquid, the mixed salt solution and urea is 7.5:17:17.

[0076] (3) Preparation of the composite material by spin coating method

[0077] The eicosanoic acid modified carbon quantum dots are mixed with deionized water to prepare a carbon quantum dot suspension liquid, and the intercalation modified MXene is mixed with deionized water to prepare an MXene suspension liquid. Then the carbon quantum dot suspension liquid and the MXene suspension liquid are mixed, ammonia water is used to adjust the pH to 8.7, and then a polyethylene glycol octylphenyl ether solution is added and stirred for 10 h to obtain a composite liquid. The rotation speed is controlled at 3500 r / min, spin coating is carried out, the temperature is controlled at 85 DEG C after spin coating, and drying is carried out in a vacuum drying oven for 16 h. The temperature is controlled at 425 DEG C after drying, annealing is carried out in an argon atmosphere, the annealing time is controlled at 2.5 h, and the carbon quantum dot MXene composite material is obtained after annealing.

[0078] The concentration of the eicosanoic acid modified carbon quantum dots in the carbon quantum dot suspension liquid is 2.25 mg / mL;

[0079] The concentration of the intercalation modified MXene in the MXene suspension liquid is 5.5 mg / mL;

[0080] The volume ratio of the carbon quantum dot suspension liquid to the MXene suspension liquid is 1:2.5.

[0081] The addition amount of the polyethylene glycol octylphenyl ether solution is 0.125% of the total volume of the carbon quantum dot suspension liquid and the MXene suspension liquid.

[0082] Comparative Example 1

[0083] Different from example 1, the step of preparing eicosanoic acid modified carbon quantum dots is omitted, and the untreated nitrogen element doped lignin carbon quantum dots are directly used as raw materials, the dosage is kept unchanged, and the remaining steps are kept unchanged, and the composite material is prepared by using a spin coating method.

[0084] The nitrogen element content of the nitrogen element doped lignin carbon quantum dots is 11.5 at%.

[0085] Comparative example 2

[0086] Different from example 1, the step of MXene intercalation modification is omitted, and the untreated MXene is directly used as a raw material, the dosage is kept unchanged, and the remaining steps are kept unchanged, and the composite material is prepared by using a spin coating method.

[0087] The size of the MXene is 170 nm.

[0088] Test example 1 rate performance test

[0089] The carbon quantum dot MXene composite materials of examples 1-3 and comparative examples 1-2 are subjected to rate performance tests, and a three-electrode device is used to characterize the performance of the MXene composite material, wherein a mercury / mercurous sulfate electrode is used as a reference electrode, an activated carbon film is used as a counter electrode, 3M sulfuric acid is used as an electrolyte, and the capacitances of the MXene composite material under different scan speeds are tested, and the results are shown in Table 1, and the capacitances of the MXene composite material under different current densities are tested, and the results are shown in Table 2.

[0090] Table 1

[0091]

[0092] Table 2

[0093]

[0094] Examples 1-3 use eicosanoic acid to modify carbon quantum dots, and sodium stannate and lithium sulfate are used to intercalate MXene under the action of urea, and finally a composite material is prepared by a spin coating method, and the rate performance of the material is excellent, and the capacitance can be kept high under different scan speeds and different current densities.

[0095] Comparative example 1 omits the step of preparing eicosanoic acid modified carbon quantum dots, and directly uses untreated nitrogen element doped lignin carbon quantum dots as raw materials, and lacks the modification of eicosanoic acid, which will cause the rate performance of the material to decrease, and the initial capacitance is low under different scan speeds and different current densities, but the capacitance decays slowly, and although there is still a large loss under high scan speed and high current density, the overall loss is slightly smaller.

[0096] Comparative Example 2 omits the MXene intercalation modification step, and uses untreated MXene as the raw material. The lack of intercalation of tin and lithium elements will cause the rate performance of the material to decrease. The initial capacity loss is small, but as the scan rate and current density increase, the capacity loss becomes more serious.

[0097] Test Example 2: Cycle stability test

[0098] The carbon quantum dot MXene composite materials of Examples 1-3 and Comparative Examples 1-2 were used to prepare capacitors, in which the nitrogen-doped graphene aerogel was used as the positive electrode material, and the MXene composite material was assembled into an asymmetric capacitor. Constant current charge and discharge tests were performed to test the cycle stability. The test current was 1 A, the voltage window was 0-1.8 V, and the capacity retention rate after different cycles was tested. The results are shown in Table 3.

[0099] Table 3

[0100]

[0101] Example 1-3 used eicosanoic acid to modify the carbon quantum dots, and sodium stannate and lithium sulfate were used to intercalate MXene under the action of urea. Finally, the composite material was prepared by spin coating. The material has excellent cycle stability, and can still maintain a high capacity retention rate after multiple cycles.

[0102] Comparative Example 1 omits the step of preparing eicosanoic acid-modified carbon quantum dots, and directly uses untreated nitrogen-doped lignin carbon quantum dots as the raw material. The lack of eicosanoic acid modification will cause the cycle stability of the material to decrease, and the capacity retention rate will decrease significantly after multiple cycles.

[0103] Comparative Example 2 omits the MXene intercalation modification step, and uses untreated MXene as the raw material. The lack of intercalation of tin and lithium elements will cause the cycle stability of the material to decrease, and the capacity retention rate will decrease significantly after multiple cycles.

[0104] Test Example 3: Energy density test at different power densities

[0105] The carbon quantum dot MXene composite materials of Examples 1-3 and Comparative Examples 1-2 were used to prepare capacitors, in which the nitrogen-doped graphene aerogel was used as the positive electrode material, and the MXene composite material was assembled into an asymmetric capacitor. The energy density at different power densities was tested, and the results are shown in Table 4.

[0106] Table 4

[0107]

[0108] Examples 1-3 use eicosanoic acid to modify carbon quantum dots, and use sodium stannate, lithium sulfate to intercalate MXene under the action of urea, and finally prepare composite materials by spin coating method. The material can maintain high energy density under different power densities;

[0109] Comparative Example 1 omits the step of preparing eicosanoic acid modified carbon quantum dots, and directly uses untreated nitrogen element doped lignin carbon quantum dots as raw material. The material lacks the modification of eicosanoic acid, and the initial energy density of the material decreases seriously. Moreover, with the increase of power density, the energy density decreases more seriously;

[0110] Comparative Example 2 omits the step of intercalating MXene, and uses untreated MXene as raw material. The material lacks the intercalation of tin and lithium elements, and although the initial energy density of the material decreases, the degree of decrease is not large. However, with the increase of power density, the energy density still decreases to a large extent.

Claims

1. A method for preparing a carbon quantum dot MXene composite material, characterized in that, The preparation method comprises the steps of preparing eicosanoic acid modified carbon quantum dots, MXene intercalation modification, and spin coating method for preparing a composite material. The method for preparing the eicosanoic acid modified carbon quantum dots comprises the following steps: dispersing nitrogen-doped lignin carbon quantum dots in anhydrous ethanol and ultrasonic dispersion, keeping the temperature after ultrasonic dispersion, and obtaining a carbon quantum dot dispersion liquid for standby; mixing eicosanoic acid, 1-cyclohexyl-2-morpholinoethyl carbodiimide p-toluenesulfonate and dichloromethane uniformly, and then adding them into the carbon quantum dot dispersion liquid for standby to stir; and after stirring, filtering, washing and drying, eicosanoic acid modified carbon quantum dots are obtained. The method for intercalation modification of MXene comprises the following steps: mixing MXene and deionized water and ultrasonic dispersion, obtaining a MXene dispersion liquid for standby after ultrasonic dispersion; mixing sodium stannate, lithium sulfate and deionized water and stirring until completely dissolved to obtain a mixed salt solution; mixing the MXene dispersion liquid, the mixed salt solution and urea, and performing hydrothermal reaction; and after the reaction, filtering, washing and drying, intercalation modified MXene is obtained. The method for preparing the composite material by the spin coating method comprises the following steps: mixing eicosanoic acid modified carbon quantum dots and deionized water to prepare a carbon quantum dot suspension liquid, mixing intercalation modified MXene and deionized water to prepare a MXene suspension liquid, then mixing the carbon quantum dot suspension liquid and the MXene suspension liquid, adjusting the pH with ammonia water, adding a polyethylene glycol octylphenyl ether solution, continuing to stir, obtaining a composite liquid, then spin coating the composite liquid, drying after spin coating, and annealing after drying to obtain a carbon quantum dot MXene composite material.

2. The preparation method of claim 1, wherein in the method for preparing the eicosanoic acid modified carbon quantum dots, the ultrasonic dispersion time is 15-25 min. The temperature during the keeping is controlled to be 60-70 DEG C. The stirring method is to keep the temperature at 60-70 DEG C and stir for 23-25 h.

3. The preparation method of claim 1, wherein in the method for preparing the eicosanoic acid modified carbon quantum dots, the mass ratio of the nitrogen-doped lignin carbon quantum dots to the anhydrous ethanol is 1:9-11. The nitrogen content of the nitrogen-doped lignin carbon quantum dots is 11.5 at%. The mass ratio of the carbon quantum dot dispersion liquid, the eicosanoic acid, the 1-cyclohexyl-2-morpholinoethyl carbodiimide p-toluenesulfonate and the dichloromethane during the keeping is 225-275:1.8-2.2:6.5-7.5:225-275.

4. The preparation method of claim 1, wherein in the method for intercalation modification of MXene, the ultrasonic dispersion time is 15-25 min. The hydrothermal reaction is performed at a temperature of 115-125 DEG C for 20-26 h. ​ ​ ​ 5.The method of claim 1, wherein: the mass ratio of MXene to deionized water in the method of intercalation modification of MXene is 1:9-11; the size of the MXene is 170 nm; the mass ratio of sodium stannate, lithium sulfate, and deionized water is 0.9-1.1:1.8-2.2:14-16; and the mass ratio of the MXene dispersion, the mixed salt solution, and urea is 6.5-7.5:13-17:13-17. 6.The method of claim 1, wherein: in the method of preparing the composite material by spin coating, the pH is adjusted to 8.3-8.7 using ammonia water; in the method of adding polyethylene glycol octylphenyl ether solution and continuing to stir, the stirring time is 10-14 h; in the method of spin coating, the rotation speed is controlled to 2500-3500 r / min; in the method of drying, the temperature is controlled to 75-85 ℃, and the drying is performed in a vacuum drying oven for 16-20 h; and in the method of annealing, the temperature is controlled to 375-425 ℃, the annealing is performed in an argon atmosphere, and the annealing time is controlled to 1.5-2.5 h. 7.The method of claim 1, wherein: in the method of preparing the composite material by spin coating, the concentration of eicosanoic acid modified carbon quantum dots in the carbon quantum dot suspension is 1.75-2.25 mg / mL; in the method of intercalation modification of MXene, the concentration of intercalation modified MXene in the MXene suspension is 4.5-5.5 mg / mL; the volume ratio of the carbon quantum dot suspension to the MXene suspension is 1:1.5-2.5; and the amount of polyethylene glycol octylphenyl ether solution added is 0.075-0.125% of the total volume of the carbon quantum dot suspension and the MXene suspension. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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