A carbon quantum dot-regulated closed-pore carbon material, its preparation method and application

Abstract

The present invention provides a carbon quantum dot-regulated closed-pore carbon material, a preparation method thereof and an application thereof. The method comprises the following steps: S1. An aromatic diamine compound, a dianhydride compound and carbon quantum dots are added into an organic solvent, mixed evenly, and then subjected to a hydrothermal reaction to obtain a precursor; S2. The precursor is calcined in a non-oxidizing atmosphere at 200-350 °C and 900-1300 °C in stages to obtain the closed-pore carbon material. By forming a closed-pore structure inside the hard carbon, the present invention can effectively reduce the contact between the hard carbon and the electrolyte, thereby avoiding the irreversible reaction of the electrolyte on the surface of the hard carbon. When the prepared carbon material is used as a negative electrode active material in an electrochemical energy storage device, the initial coulombic efficiency of the electrochemical energy storage device can be effectively improved, and at the same time, its plateau capacity can be effectively increased.

Description

Technical Field

[0001] The present invention relates to the technical field of anode materials, and more specifically, to a closed-pore carbon material regulated by carbon quantum dots, a preparation method thereof, and an application thereof. Background Art

[0002] Benefiting from the rich sodium reserves, environmental friendliness, and similar electrochemical properties between lithium and sodium, sodium-ion batteries are considered to be high-quality low-cost supplementary products in the future energy storage industry, and are considered to be one of the most promising alternatives to lithium-ion batteries, and are expected to be applied in large-scale energy storage and smart grids. In recent years, the state has successively issued many relevant documents to promote the commercialization of sodium-ion batteries and guide their high-quality development.

[0003] The development of advanced sodium-ion batteries relies on the construction of high-performance electrode materials. Developing low-cost and high-performance anode materials is a key link among them. Hard carbon materials, due to their rich reserves, low cost, stable structure, low sodium intercalation voltage platform and other advantages, make hard carbon the most commercially promising anode material. However, hard carbon anodes are still restricted by bottlenecks such as low first-cycle Coulomb efficiency, poor rate performance, and unsatisfactory cycle performance, and these performance indicators are key factors promoting the commercialization of sodium-ion batteries. Although a large number of optimized process methods have been used to modify the structure, composition, surface functionalization, etc. of hard carbon materials, these methods often can only improve a single property of hard carbon anodes. For example, although the reversible sodium storage capacity is increased by introducing doping defects, the first-cycle Coulomb efficiency is significantly reduced; constructing a porous structure can promote the diffusion of the electrolyte and rate performance, but the electrolyte decomposition is aggravated and the first-cycle Coulomb efficiency is also significantly reduced; reducing defects and porosity can improve the first-cycle Coulomb efficiency and stabilize the electrode-electrolyte interface, but the reversible capacity and rate performance cannot be guaranteed; or by depositing a coating layer on the surface of hard carbon, the contact between the electrolyte and the electrode surface can be blocked, so the electrolyte decomposition can be alleviated and the electrode-electrolyte interface can be optimized, thereby improving the first-cycle Coulomb efficiency and reversible capacity; however, due to the deposited coating layer being non-conductive and electrochemically inactive, the rate performance and cycle performance of the battery are still unsatisfactory. In addition, the reported or studied surface coating methods require very complex equipment, the operation process is cumbersome, and it is impossible to controllably form a uniform coating film on the surface of hard carbon.

[0004] Therefore, it is urgent to develop more effective optimization strategies to multi-dimensionally improve the sodium storage performance of hard carbon anodes to promote the commercial application of sodium-ion batteries based on hard carbon anodes. Summary of the Invention

[0005] Based on the above technical problems existing in the prior art, one of the objectives of the present invention is to provide a preparation method of a carbon quantum dot-regulated closed-pore carbon material. By forming a closed-pore structure inside the hard carbon, this method can effectively reduce the contact between the hard carbon and the electrolyte, thereby avoiding the irreversible reaction of the electrolyte on the surface of the hard carbon. When the prepared carbon material is used as the negative electrode active material in an electrochemical energy storage device, it can effectively improve the first-cycle Coulombic efficiency of the electrochemical energy storage device and simultaneously effectively improve its plateau capacity.

[0006] To achieve the above objective, the technical solution of the present invention is as follows:

[0007] A preparation method of a carbon quantum dot-regulated closed-pore carbon material, comprising the following steps:

[0008] S1. Add an aromatic diamine compound, a dianhydride compound, and carbon quantum dots into an organic solvent, mix evenly, and then carry out a hydrothermal reaction to obtain a precursor;

[0009] S2. Calcinate the precursor in a non-oxidizing atmosphere at 200 - 350 °C and 900 - 1300 °C in stages to obtain the closed-pore carbon material.

[0010] In some embodiments, in step S1, the aromatic diamine compound is at least one of benzidine, 3,3'-dichlorobenzidine, 3,3'-dimethoxybenzidine, and 3,3'-dimethylbenzidine.

[0011] In some embodiments, in step S1, the dianhydride compound is at least one of 5,5'-carbonylbis(isobenzofuran-1,3-dione), pyromellitic dianhydride, mellitic anhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, and 2,3,3',4'-diphenylethertetracarboxylic dianhydride.

[0012] In some embodiments, in step S1, the organic solvent is at least one of ethanol, ether, acetone, tetrahydrofuran, and dimethylformamide.

[0013] In some embodiments, in step S1, the temperature of the hydrothermal reaction is 120 - 180 °C.

[0014] In some embodiments, in step S1, the mass ratio of the aromatic diamine compound to the dianhydride compound is 1:1.5 - 2.

[0015] In some embodiments, in step S1, the carbon quantum dots are 0.5-10% of the total mass of the reaction raw materials. Preferably, it is 0.5-7%. By adding carbon quantum dots, the number of closed pores in the generated hard carbon material is regulated. If too few carbon quantum dots are added, it is likely to result in fewer closed pore structures in the carbon material, thereby restricting the performance of the carbon material's platform capacity. If too many are added, the proportion of the platform capacity becomes too large, restricting the fast reaction kinetics corresponding to the sodium storage process in the carbon material and causing the rate performance of the material to not meet the requirements of actual use.

[0016] In some embodiments, in step S1, the reaction raw materials are added to an organic solvent and stirred at 20-30°C for 8-12 h.

[0017] In some embodiments, in step S2, the temperature is raised to 200-350°C at a heating rate of 2-10°C / min.

[0018] In some embodiments, in step S2, the temperature is raised to 900-1300°C at a heating rate of 2-10°C / min.

[0019] In some embodiments, the non-oxidizing atmosphere includes a reducing atmosphere, an inert gas atmosphere, or a protective gas atmosphere, including but not limited to, a nitrogen atmosphere, a hydrogen atmosphere, an argon atmosphere, etc.

[0020] One object of the present invention is to provide a closed-pore carbon material, which is made by the preparation method of any of the above embodiments.

[0021] In some embodiments, the ratio of the peak area of the defect peak to the graphite peak in the closed-pore carbon material is 2.0-3.0:1.

[0022] Another object of the present invention is to provide a negative electrode material, which includes the above-mentioned closed-pore carbon material.

[0023] A third object of the present invention is to provide a negative electrode, which includes the above-mentioned negative electrode material.

[0024] A fourth object of the present invention is to provide an electrochemical energy storage device, which includes the above-mentioned negative electrode.

[0025] Specifically, the energy storage device includes but is not limited to sodium ion batteries, sodium ion capacitors, etc.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] In the present invention, carbon quantum dots are used as additives for the closed-pore structure. The precursor is obtained by hydrothermal reaction of reaction raw materials, and then calcined in segments at a specific temperature to obtain a carbon material with a closed-pore structure. The ratio of the peak area of the defect peak to the graphite peak of the carbon material is 2.0 - 3.0:1. By introducing the closed-pore structure, on the one hand, the carbon material can play its sodium storage role in the low-voltage plateau region, thus significantly increasing the plateau capacity. On the other hand, the contact area between the electrode and the electrolyte is reduced, which can avoid the reduction of the first-cycle Coulombic efficiency.

[0028] In addition, the preparation method of the present invention can effectively regulate the number of closed pores and the degree of graphitization of the carbon material by the addition amount of carbon quantum dots and the calcination temperature, effectively coordinate the two parameters, and give full play to the plateau capacity and improve the first-cycle Coulombic efficiency.

[0029] In addition, the preparation method of the present invention has a simple process flow, a short preparation time, and a low raw material cost, and is suitable for industrial production. Description of the Drawings

[0030] Figure 1 It is the TEM image of the closed-pore carbon material prepared in Example 1 of the present invention;

[0031] Figure 2 It is the pore size distribution diagram of the closed-pore carbon material prepared in Example 1 of the present invention;

[0032] Figure 3 It is the Raman image of the closed-pore carbon material prepared in Example 1 of the present invention;

[0033] Figure 4 It is the charge-discharge curve of the closed-pore carbon material prepared in Example 1 of the present invention at a current density of 100 mA / g;

[0034] Figure 5 It is the cycle curve of the closed-pore carbon material prepared in Example 1 of the present invention after 150 cycles at a current density of 100 mA / g;

[0035] Figure 6 It is the TEM image of the closed-pore carbon material prepared in Example 2 of the present invention;

[0036] Figure 7 It is the first-cycle charge-discharge curve of the closed-pore carbon material prepared in Example 2 of the present invention at a current density of 100 mA / g;

[0037] Figure 8 It is the cycle curve of the closed-pore carbon material prepared in Example 2 of the present invention after 150 cycles at a current density of 100 mA / g;

[0038] Figure 9 It is the TEM image of the closed-pore carbon material prepared in Comparative Example 1 of the present invention;

[0039] Figure 10 The first charge-discharge curve of the closed-cell carbon material prepared in Comparative Example 1 of the present invention at a current density of 100 mA / g;

[0040] Figure 11 The cycle curve of the closed-cell carbon material prepared in Comparative Example 1 of the present invention after 150 cycles at a current density of 100 mA / g. Detailed implementation manners

[0041] Many specific details are set forth in the following description in order to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific implementations disclosed below.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this invention belongs. The terms used in the specification of the present invention herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention.

[0043] Example 1

[0044] A preparation method of a closed-cell carbon material, comprising the following steps:

[0045] S1. Dissolve 3.68 g of benzidine in 120 mL of dimethylformamide, then add 6.44 g of 5,5'-carbonylbis(isobenzofuran-1,3-dione) and 500 mg of carbon quantum dots to the above solution, and magnetically stir at room temperature for 12 h to obtain a PAA solution; then transfer the PAA solution into a high-pressure reaction kettle and carry out a hydrothermal reaction at 180°C for 10 h; after the reaction is completed, cool to room temperature to obtain a suspension; wash the obtained suspension with ethanol several times, and then place it in a vacuum oven and dry at 90°C for 12 h to obtain a precursor powder;

[0046] S2. Transfer the precursor powder obtained in step S1 into a tubular furnace, and under an argon atmosphere, heat it to 350°C at a heating rate of 5°C / min for pre-calcination for 1 h; then heat it to 1200°C at a heating rate of 5°C / min for calcination for 2 h; after the calcination is completed, naturally cool to room temperature to obtain a closed-cell carbon material rich in closed-cell structure (named: PNDCs@CDs-1200°C).

[0047] Perform TEM testing, nitrogen adsorption-desorption testing, and Raman testing on the obtained closed-cell carbon material, and the test results are respectively as Figure 1 , Figure 2 and Figure 3 shown.

[0048] Among them,Figure 1 This is the TEM image of the closed-cell carbon material. Figure 2 This is the pore size distribution diagram of the closed-cell carbon material. Figure 3 This is the Raman image of the closed-cell carbon material.

[0049] As Figure 1 shown, the PNDCs@CDs-1200℃ obtained in this example is rich in a large number of mesoporous structures.

[0050] As Figure 2 shown, the PNDCs@CDs-1200℃ obtained in this example contains open micropores that can be penetrated by nitrogen, but the material internally contains a large number of closed-cell structures that cannot be detected by nitrogen.

[0051] As Figure 3 shown, for the PNDCs@CDs-1200℃ obtained in this example, the ratio of the peak area of the defect peak to the graphite peak is 2.28, indicating the amorphous nature of the closed-cell carbon.

[0052] The obtained PNDCs@CDs-1200℃ was subjected to relevant electrochemical performance tests. The specific method is as follows:

[0053] Assemble the battery: The PNDCs@CDs-1200℃ obtained in this example was mixed with the binder carboxymethyl cellulose (CMC) and the conductive agent Super P (SP) in a mass ratio of 70:15:15 to form a homogeneous slurry, which was then coated on a copper foil to make a negative electrode sheet; in a vacuum glove box, a sodium metal sheet was placed at the negative electrode shell end, Whatman GF / D was used as the separator, and 1 mol / L NaClO4 / PC + FEC (5%) was used as the electrolyte to assemble a CR2016 coin cell, and its electrochemical performance was tested. The test results are as Figure 4 and Figure 5 shown.

[0054] As Figure 4 shown, for the half-cell assembled with the PNDCs@CDs-1200℃ obtained in this example as the negative electrode active material, an obvious low voltage plateau below 0.1 V appears. At a current density of 100 mA / g, the plateau capacity is 134 mAh / g, and the initial coulombic efficiency is 68.4%.

[0055] As Figure 5 shown, for the half-cell assembled with the PNDCs@CDs-1200℃ obtained in this example as the negative electrode active material, after 150 cycles at a current density of 100 mA / g, the specific capacity is 221 mAh / g, and the coulombic efficiency remains at 99.7%, indicating good cycle stability.

[0056] Example 2

[0057] A preparation method of a closed-cell carbon material, comprising the following steps:

[0058] S1. Dissolve 3.68 g of benzidine in 120 mL of dimethylformamide, then add 6.44 g of 5,5'-carbonylbis(isobenzofuran-1,3-dione) and 500 mg of carbon quantum dots into the above solution, and magnetically stir for 12 h at room temperature to obtain a PAA solution; then transfer the above PAA solution into a high-pressure reactor and carry out hydrothermal reaction at 180 °C for 10 h; after the reaction is completed, cool to room temperature to obtain a suspension; wash the obtained suspension several times with ethanol, and then place it in a vacuum oven and dry at 90 °C for 12 h to obtain a precursor powder;

[0059] S2. Transfer the precursor powder obtained in step S1 into a tubular furnace, and under an argon atmosphere, heat it to 350 °C at a heating rate of 5 °C / min for pre-calcination for 1 hour, and then heat it to 900 °C at a heating rate of 5 °C / min for calcination for 2 h; after the calcination is completed, naturally cool to room temperature to obtain a closed-cell carbon material rich in closed-cell structure (named: PNDCs@CDs).

[0060] The prepared closed-cell carbon material was subjected to TEM testing, and the test results are as Figure 6 shown; at the same time, the method of Example 1 was used to test its electrochemical performance, and the test results are as Figure 7 and Figure 8 shown.

[0061] As Figure 6 shown, the PNDCs@CDs prepared in this example have a relatively large number of closed pores, but due to the relatively low calcination temperature, the open pores of the carbon material cannot be further converted into closed pores; after testing, the ratio of the peak area of its defect peak to the graphite peak is 2.98.

[0062] As Figure 7 shown, for the half-cell assembled with the PNDCs@CDs prepared in this example as the negative electrode active material, there is also an obvious low voltage plateau below 0.1 V. At a current density of 100 mA / g, the plateau capacity is 108 mAh / g, and the first-cycle Coulombic efficiency is 62.3%.

[0063] As Figure 8 shown, for the half-cell assembled with the PNDCs@CDs prepared in this example as the negative electrode active material, at a current density of 100 mA / g, after 150 cycles, the specific capacity is 195 mAh / g, and the Coulombic efficiency still remains at 99.6%, indicating its good cycle stability.

[0064] Comparative Example 1

[0065] A preparation method of a closed-cell carbon material, comprising the following steps:

[0066] S1. Dissolve 3.68 g of benzidine in 120 mL of dimethylformamide, and then add 6.44 g of 5,5'-carbonylbis(isobenzofuran-1,3-dione) to the above solution. Stir magnetically at room temperature for 12 h to obtain a PAA solution. Then transfer the above PAA solution into a high-pressure reactor and carry out hydrothermal reaction at 180 °C for 10 h. After the reaction is completed, cool it to room temperature to obtain a suspension. Wash the obtained suspension several times with ethanol, and then place it in a vacuum oven and dry it at 90 °C for 12 h to obtain a precursor powder.

[0067] S2. Transfer the precursor powder obtained in step S1 into a tubular furnace. Under an argon atmosphere, heat it to 350 °C at a heating rate of 5 °C / min and pre-calcine for 1 h, and then heat it to 900 °C at a heating rate of 5 °C / min and calcine for 2 h. After the calcination is completed, cool it naturally to room temperature to obtain a hard carbon material (named: PNDCs).

[0068] The hard carbon material prepared in this comparative example was subjected to TEM testing, and the test results are as Figure 9 shown; at the same time, electrochemical performance testing was carried out, and the test results are as Figure 10 and Figure 11 shown.

[0069] As Figure 9 shown, the microstructure of the PNDCs prepared in this example hardly contains closed pores.

[0070] As Figure 10 shown, for the half-cell assembled with the PNDCs prepared in this example as the negative electrode active material, there is no obvious low voltage platform below 0.1 V, and due to the lack of a closed pore structure, the irreversible reaction with the electrolyte cannot be avoided. At a current density of 100 mA / g, the platform capacity is 64 mAh / g, and the first-cycle Coulombic efficiency is only 54.7%.

[0071] As Figure 11 shown, for the half-cell assembled with the PNDCs prepared in this example as the negative electrode active material, at a current density of 100 mA / g, after 150 cycles, due to the lack of closed pores, it cannot provide sodium storage sites in the low voltage platform range, and the specific capacity is only 159 mAh / g.

[0072] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0073] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A preparation method of a closed-pore carbon material regulated by carbon quantum dots, characterized in that It includes the following steps: S1. Add an aromatic diamine compound, a dianhydride compound and carbon quantum dots into an organic solvent, mix them evenly, and then carry out a hydrothermal reaction to obtain a precursor; S2. Calcinate the precursor in a non-oxidizing atmosphere at 200 - 350 °C and 900 - 1300 °C in stages to obtain the closed-cell carbon material; The carbon quantum dots are 0.5 - 10% of the total mass of the reaction raw materials.

2. The preparation method of the closed-pore carbon material regulated by carbon quantum dots according to claim 1, wherein, In step S1, the aromatic diamine compound is at least one of benzidine, 3,3'-dichlorobenzidine, 3,3'-dimethoxybenzidine, 3,3'-dimethylbenzidine; and / or, the dianhydride compound is at least one of 5,5'-carbonylbis(isobenzofuran-1,3-dione), pyromellitic dianhydride, benzene-1,2,4,5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,3',4'-diphenylethertetracarboxylic dianhydride; and / or, the organic solvent is at least one of ethanol, ether, acetone, tetrahydrofuran, dimethylformamide.

3. The preparation method of the closed-pore carbon material regulated by carbon quantum dots according to claim 1, wherein, In step S1, the temperature of the hydrothermal reaction is 120 - 180 °C.

4. The preparation method of the closed-cell carbon material according to claim 1, characterized in that The mass ratio of the aromatic diamine compound to the dianhydride compound is 1:1.5 - 2.

5. The preparation method of the closed-cell carbon material regulated by carbon quantum dots according to claim 1, wherein In step S2, heat up to 200 - 350 °C at a heating rate of 2 - 10 °C / min; and / or, heat up to 600 - 1300 °C at a heating rate of 2 - 10 °C / min.

6. A closed-cell carbon material, characterized in that, Prepared by the preparation method according to any one of claims 1 - 5.

7. A negative electrode material, characterized in that, It includes the closed-cell carbon material according to claim 6.

8. Negative electrode, characterized in that, It includes the negative electrode material according to claim 7.

9. An electrochemical energy storage device, characterized in that, It includes the negative electrode according to claim 8.

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