Cobalt monatomic modified carbon nanosheet, preparation method and application of cobalt monatomic modified carbon nanosheet in potassium ion battery

Abstract

The invention relates to the technical field of energy storage, in particular to a cobalt monatomic modified carbon nanosheet, a preparation method and application of the cobalt monatomic modified carbon nanosheet in a potassium ion battery, carbonyl coal pitch, cobalt nitrate, boric acid and urea are mixed in deionized water, dried and then transferred into a carbonization furnace, and the cobalt monatomic modified carbon nanosheet is prepared through calcination in the argon atmosphere. Cobalt monatomic not only provides abundant active sites for the carbon nanosheets and enhances the reversible adsorption capacity to potassium ions, but also catalyzes the carbon nanosheets to form a partially graphitized structure and enhances the electronic conductivity; the ultrathin carbon nanosheets shorten the diffusion distance of ions and effectively enhance the diffusion efficiency of potassium ions. Therefore, the obtained potassium ion battery shows high specific capacity and good cycling stability. The whole process avoids the pickling step required by the metal monatomic doped carbon material, has the advantages of simplicity and low cost, and provides a new preparation method for the potassium ion battery based metal monatomic modified carbon negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, specifically to a cobalt single-atom modified carbon nanosheet, its preparation method, and its application in potassium-ion batteries. Background Technology

[0002] Potassium is abundant and widely distributed on Earth, making potassium-ion batteries a promising alternative to lithium-ion batteries. Despite significant progress in potassium-ion battery research, their poor electrochemical performance is hampered by issues such as substantial electrode volume expansion due to large potassium ion (1.38 Å) insertion / extraction and slow reaction kinetics during cycling. These factors hinder the practical application of potassium-ion batteries with high energy density and long cycle life. Exploring suitable electrode materials for potassium-ion batteries, especially anode materials with robust structures, excellent rate performance, and good cycle life, remains a challenging task.

[0003] Carbon materials are considered highly promising anode materials for potassium-ion batteries due to their stable operating voltage (0-3 V), tunable structure, and abundant resources. Among them, non-graphitized hard carbon with a large interlayer spacing can effectively adapt to potassium. + The volume change during the insertion / extraction process, coupled with the presence of more potassium storage active sites, offers advantages such as high capacity and long-term cycling stability, thus attracting widespread attention. However, most hard carbon materials exhibit low intrinsic electronic conductivity, leading to poor battery performance at high current densities. Therefore, research typically employs strategies such as heteroatom doping, microstructure manipulation, and surface modification to enhance their conductivity. For example, introducing heteroatoms such as nitrogen, sulfur, and boron can tune the electronic structure of carbon materials, thereby improving conductivity. However, these methods often introduce a significant amount of sp atoms onto the material surface. 3 Defects disrupt the π-π conjugated system of the carbon network, which may actually lead to a further decrease in conductivity. Therefore, achieving a balance between the electronic conductivity of hard carbon materials and the defect structure and effective porosity of the carbon matrix is ​​a challenge.

[0004] Single-atom doped materials, which anchor single metal atoms onto conductive carriers, have played an important role in electrocatalysis and energy storage. Single-atom doped materials can maximize the utilization efficiency of metal atoms and break through the size limit of traditional nanoparticles. Constructing single-atom doped carbon materials with atomically dispersed metal sites in carbon materials has the following potential advantages: (1) Metal centers and their coordination environment (such as M–N) x M–Cᵧ) can provide abundant active sites, enhancing the response to K +(1) Reversible adsorption of metal atoms reduces the reaction energy barrier; (2) The strong interaction between metal atoms and carbon substrate can not only stabilize the dispersion state of metal single atoms, but also regulate the local electronic structure, promote charge transfer, and inhibit the aggregation of metal atoms during the cycling process; (3) The introduction of metal single atoms can catalyze the formation of partially graphitized carbon materials in the subsequent carbonization process, thereby enhancing electronic conductivity; (4) Single atom sites can enhance the adsorption of K. + The affinity of nitrogen atoms for alkali metals reduces ion migration resistance, thereby improving rate performance. However, previous studies have shown that the symmetrical neighboring nitrogen atoms surrounding conventional single-atom doped carbon materials with symmetrical electron distribution can hinder the adsorption of alkali metal ions. Therefore, it is necessary to introduce additional heteroatoms to adjust the interface configuration of the central metal atom, breaking the symmetry of the electron density of the MNC active site, thereby enhancing the adsorption capacity for alkali metal ions. More importantly, the preparation process of most single-atom doped carbon materials inevitably involves a final acid washing step to remove metal atom clusters or particles, which not only increases the complexity of carbon material preparation but also creates requirements for waste acid treatment. Therefore, how to rationally design and construct single-atom doped carbon materials with asymmetric coordination structures in the carbon framework using simple and green methods, in order to simultaneously achieve high capacity, excellent rate performance, and cycle stability in potassium-ion batteries, is crucial for the practical application of single-atom doped carbon materials.

[0005] In view of the above-mentioned defects, the inventors of this invention have finally obtained this invention after a long period of research and practice. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of low potassium storage capacity, poor rate performance and insufficient cycle stability of carbon anodes in potassium-ion batteries. It provides a cobalt single-atom modified carbon nanosheet, its preparation method and its application in potassium-ion batteries.

[0007] To achieve the above objectives, this invention discloses a method for preparing cobalt single-atom modified carbon nanosheets, comprising the following steps:

[0008] S1, carbonyl coal tar pitch is dispersed in deionized water, cobalt nitrate hexahydrate is added, the mixture is heated to 60°C and stirred for 12 hours, then the mixture is filtered and washed several times with deionized water to obtain carbonyl coal tar pitch@cobalt ions;

[0009] S2, disperse the carbonyl coal tar pitch@cobalt ions obtained in step S1 in deionized water, add boric acid and urea, stir for 6 hours, and then dry the mixture in a forced-air drying oven at 80°C to obtain a solid mixture;

[0010] S3. The solid mixture obtained in step S2 is placed in a tube furnace and carbonized at high temperature under an inert gas atmosphere to obtain cobalt single-atom modified carbon nanosheets.

[0011] In step S1, the preparation method of carbonyl coal tar pitch includes the following steps:

[0012] S11, after stirring coal tar pitch and tetrahydrofuran solvent for 12 hours, the tetrahydrofuran insoluble matter is removed by centrifugation. The tetrahydrofuran soluble matter is removed by heating and stirring at 80°C to remove the tetrahydrofuran solvent. Then, 1,2-dichloroethane solution is added to dissolve the tetrahydrofuran soluble matter to obtain a mixed solution.

[0013] S12, add 1,2-dichloroethane solution to anhydrous aluminum trichloride, sonicate for 1 hour, and then continue to stir magnetically for 4 hours to form a viscous mixture;

[0014] S13, place the viscous mixture obtained in step S12 in an ice bath. When the temperature of the viscous mixture drops to 0°C, add oxaloyl chloride at a rate of 1 drop / s. After the addition is complete, continue stirring the reaction for 1 hour.

[0015] S14, when the mixture after the reaction in step S13 is heated to 20°C, the mixed solution obtained in step S11 is slowly added and the mixture is stirred for 12 hours.

[0016] S15, the reaction product from step S14 is poured into an ice-water mixture, filtered and washed multiple times, and finally dried under vacuum at 80°C to obtain carbonyl coal tar pitch.

[0017] In step S11, the mass of coal tar pitch used is 5-20g, the volume of tetrahydrofuran used is 150-500mL, and the volume of 1,2-dichloroethane solution used is 200-500mL.

[0018] In step S12, the mass of anhydrous aluminum trichloride used is 10-30g, the volume of 1,2-dichloroethane used is 100-400mL, and the mass of oxaloyl chloride used is 30-100g.

[0019] In step S1, the mass ratio of carbonyl coal tar pitch to cobalt nitrate hexahydrate is 1:0.02~0.2.

[0020] In step S2, the mass ratio of carbonyl coal tar pitch @ cobalt ions, urea and boric acid is 1:3~8:0~0.6.

[0021] In step S3, the inert gas is argon or nitrogen, the gas flow rate is 300 mL / min, the heating rate is 5 °C / min, the high-temperature carbonization temperature is 800 °C, and the time is 2 h.

[0022] The present invention also discloses cobalt single-atom modified carbon nanosheets prepared by the above preparation method.

[0023] This invention also discloses the application of the above-mentioned cobalt single-atom modified carbon nanosheets in potassium-ion batteries, wherein the preparation of the potassium-ion battery includes the following steps:

[0024] A1. Place polyvinylidene fluoride (10 mg) in a grinding jar, add 200 μL of N-methylpyrrolidone and stir. Then continue to add cobalt single-atom modified carbon nanosheets (70 mg) and conductive carbon black (20 mg) to the grinding jar and continue grinding and mixing. During this process, N-methylpyrrolidone is added dropwise to form a uniform paste.

[0025] A2, Transfer the slurry obtained in step A1 to a cut copper foil current collector (20*7.5cm). 2 One end of the copper foil is coated with a scraper to form a film. The coated copper foil is then placed in a vacuum drying oven and dried at 90°C for 12 hours. After drying, it is cut into circular electrode sheets (13.14 mm in diameter).

[0026] A3. Assemble the circular electrode sheet, separator, and potassium metal sheet prepared in step A2 into a potassium ion half cell, and drop 100 μL of 0.8 M potassium hexafluorophosphate electrolyte onto the separator.

[0027] The loading of cobalt-modified carbon nanosheets in the circular electrode sheet is 0.8~1.5 mg / cm³. 2 .

[0028] By utilizing the oxygen atom of the carbonyl group as a strong coordinating site, cobalt ions (Co) are anchored in situ and uniformly in solution. 2+ This lays the foundation for the formation of highly dispersed cobalt single atoms during subsequent pyrolysis. The carbonyl oxygen has a negative charge; therefore, the oxygen atom in the carbonyl group can act as a strong coordination site. Under the influence of electrostatic forces in the solution, cobalt ions are adsorbed by the carbonyl oxygen, thus achieving the cobalt ion (Co)... 2+ The cobalt single atoms are in situ and uniformly anchored, and during the subsequent pyrolysis process, they combine in situ with carbon, nitrogen and boron atoms to form highly dispersed cobalt single atoms.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. This invention provides a method for preparing cobalt single-atom modified carbon nanosheets. The method employs a simple liquid-phase adsorption and high-temperature carbonization strategy, using carbonyl coal tar pitch as the carbon source, and cobalt nitrate, boric acid, and urea as the cobalt, boron, and nitrogen sources, respectively. The carbonyl coal tar pitch, cobalt nitrate, boric acid, and urea are mixed in deionized water and dried before being transferred to a carbonization furnace. Under an argon atmosphere, the mixture is heated to prepare cobalt single-atom modified carbon nanosheets. The method is simple, involving only mixing, drying, and high-temperature carbonization steps, and is environmentally friendly.

[0031] 2. The material obtained by the preparation method of the present invention has a wide carbon interlayer spacing, a high microporous specific surface area and an ultrathin two-dimensional carbon sheet structure, which can realize the rapid insertion / extraction of potassium ions and provide a large number of adsorption and desorption active sites for potassium ions. Furthermore, through the affinity of cobalt single atoms for potassium ions, the diffusion reaction kinetics of potassium ions are accelerated.

[0032] 3. The cobalt single-atom modified carbon nanosheet material prepared by this invention effectively exposes high-activity sites and improves the diffusion efficiency of potassium ions because the single-atom cobalt is uniformly distributed on the surface of the two-dimensional ultrathin carbon nanosheets; thus effectively improving the cycle stability and rate performance of potassium-ion batteries.

[0033] 4. The cobalt single-atom modified carbon nanosheet material prepared by this invention has high capacity, excellent cycle performance and rate performance when applied in potassium-ion batteries. Attached Figure Description

[0034] Figure 1 The XRD patterns are of the cobalt single-atom modified carbon nanosheets obtained in Example 1 and the materials obtained in Examples 2-5;

[0035] Figure 2 SEM images of the cobalt single-atom modified carbon nanosheets (c-d) obtained in Example 1 and the materials obtained in Comparative Examples 1 (a-b) and 2 (e-f);

[0036] Figure 3 TEM images of the carbon nanotube material modified with cobalt single atoms obtained in Example 1: (a) 50 nm, (b) 20 nm, (c) 5 nm;

[0037] Figure 4 The nitrogen adsorption / desorption curves of the cobalt single-atom modified carbon nanotubes obtained in Example 1 are shown.

[0038] Figure 5 The following are synchrotron radiation data and fitting results for Example 1 and the control standards: cobalt foil, cobalt trioxide, and cobalt phthalocyanine. (a) shows the cobalt K-edge XANES spectra of Example 1, cobalt foil, cobalt trioxide, and cobalt phthalocyanine; (b) shows the k-edge XANES spectra of cobalt foil, cobalt trioxide, cobalt phthalocyanine, and Example 1 at the cobalt K-edge. 3 Weighted Fourier transform curves, (c) wavelet transform WT profile of EXAFS signals of cobalt foil, cobalt trioxide, cobalt phthalocyanine and Example 1, (d) cobalt K-edge EXAFS spectra of cobalt foil, cobalt trioxide, cobalt phthalocyanine and Example 1 in k-space, (e) k-edge EXAFS spectra of Example 1 in R-space. 3 Weighted Fourier Transform EXAFS and its corresponding FT-EXAFS fitting curve;

[0039] Figure 6The rate performance of the materials obtained in Examples 1-5 and Comparative Examples 1-2 when applied to potassium-ion batteries;

[0040] Figure 7 The cycling performance of the materials obtained in Examples 1-5 in potassium-ion batteries at 2 A / g is shown. Detailed Implementation

[0041] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings.

[0042] Example 1

[0043] The first step, the preparation method of carbonyl coal tar pitch, is as follows:

[0044] 10 g of coal tar pitch was mixed with 300 mL of tetrahydrofuran for 12 h, and the insoluble matter was removed by centrifugation. Next, the soluble matter was heated at 80 °C with stirring to remove the tetrahydrofuran solvent. Then, 200 mL of 1,2-dichloroethane solution was added and stirred to dissolve the tetrahydrofuran soluble matter, forming mixture A. 20 g of anhydrous aluminum trichloride was placed in a three-necked flask, and 300 mL of 1,2-dichloroethane solution was added. After sonication for 1 h, magnetic stirring was continued for 4 h to form a viscous mixture. The three-necked flask containing the viscous mixture was placed in a water bath containing an ice-water mixture. When the temperature of the viscous mixture dropped to 0 °C, 50 g of oxaloyl chloride was added at a rate of drop per second. After the addition was complete, the reaction was continued with stirring for 1 h to form mixture B. In the water bath, the reaction mixture B was heated to 20 °C, and mixture A was slowly added. The reaction was continued with stirring for 12 h. Finally, the reaction product was poured into an ice-water mixture, filtered and washed multiple times, and then vacuum dried at 80°C to obtain carbonyl coal tar pitch material.

[0045] The second step, the preparation method of cobalt single-atom modified carbon nanosheets, is as follows:

[0046] Carbonyl coal tar pitch was dispersed in 40 mL of deionized water, and 0.1 g of cobalt nitrate hexahydrate was added. The mixture was heated to 60 °C and stirred for 12 h. The mixture was then filtered and washed several times with deionized water to obtain carbonyl coal tar pitch adsorbed with cobalt ions. This cobalt-adsorbed carbonyl coal tar pitch was dispersed in 50 mL of deionized water, and 0.3 g of boric acid and 5 g of urea were added. After stirring for 6 h, the mixture was dried in an 80 °C oven and ground in a mortar. It was then placed in a tube furnace and calcined at 800 °C for 2 h in an argon atmosphere at a heating rate of 5 °C / min to obtain cobalt single-atom modified carbon nanosheets, denoted as CoBN-CNS. 800Synchrotron radiation tests were performed on the cobalt foil, cobalt trioxide, and cobalt phthalocyanine samples of Example 1 and the control standard to determine the asymmetric coordination structure of Co-B1N3 in Example 1.

[0047] Figure 5 The figures show synchrotron radiation data and fitting results for Example 1 and the control standard samples cobalt foil, cobalt trioxide, and cobalt phthalocyanine. Figure 5 (a) The cobalt K-edge XANES spectrum shows that the pre-edge peak of Example 1 and cobalt phthalocyanine is located at 7709 eV, indicating that they both have similar cobalt coordination configurations of a Co-N4 square planar structure. In addition, the near-edge position of Example 1 is between that of the cobalt foil and cobalt trioxide, indicating that its valence state is between 0 and +3. Figure 5 (b) Shows the k-values ​​of the FT-EXAFS spectra of cobalt foil, cobalt trioxide, cobalt phthalocyanine, and Example 1. 3 The weighted Fourier transform curves showed that the cobalt K FT-EXAFS of Example 1 exhibited a peak position containing cobalt phthalocyanine at 1.55 Å, which is mainly related to the shell scattering of the Co-N / B bond. Figure 5 (c) The WT profiles of cobalt foil, cobalt trioxide, cobalt phthalocyanine, and Example 1 show that, under the influence of the Co-N and Co-B coordination structures, the WT profile of Example 1 at 3.6 Å -1 The maximum intensity is observed at this location. k in Example 1 2 The shape of the χ(k) oscillation curve is similar to that of cobalt phthalocyanine, but their oscillation frequencies are different, which further indicates that their coordination configurations are somewhat similar. Figure 5 (d)). Finally, by performing EXAFS fitting on Example 1 ( Figure 5 (e) The coordination numbers of boron and nitrogen atoms were determined to be 1.2 and 3.1, respectively, proving that the central cobalt atom in Example 1 formed a coordination structure with three nitrogen atoms and one boron atom (as shown in Table 1 below).

[0048] Table 1. EXAFS fitting parameters of the cobalt K energy edge in Example 1

[0049]

[0050] Note: CN, coordination number; R, distance between the absorber and the backscattering atom; σ 2 , used to account for thermal and structural disturbances in the Debye-Waller factor; ΔE0, internal potential correction value; R-value indicates the accuracy of the fit. For cobalt, It was fixed at 0.76. The reasonable range for EXAFS fitting parameters: 0.700 < < 1.000; CN > 0; σ 2 Å 2> 0; |ΔE0| < 15 eV; R value < 0.02.

[0051] Example 2

[0052] The first step, the preparation method of carbonyl coal tar pitch, is as follows:

[0053] 10 g of coal tar pitch was mixed with 300 mL of tetrahydrofuran for 12 h, and the insoluble matter was removed by centrifugation. Next, the soluble matter was heated at 80 °C with stirring to remove the tetrahydrofuran solvent. Then, 200 mL of 1,2-dichloroethane solution was added and stirred to dissolve the tetrahydrofuran soluble matter, forming mixture A. 20 g of anhydrous aluminum trichloride was placed in a three-necked flask, and 300 mL of 1,2-dichloroethane solution was added. After sonication for 1 h, magnetic stirring was continued for 4 h to form a viscous mixture. The three-necked flask containing the viscous mixture was placed in a water bath containing an ice-water mixture. When the temperature of the viscous mixture dropped to 0 °C, 50 g of oxaloyl chloride was added at a rate of drop per second. After the addition was complete, the reaction was continued with stirring for 1 h to form mixture B. In the water bath, the reaction mixture B was heated to 20 °C, and mixture A was slowly added. The reaction was continued with stirring for 12 h. Finally, the reaction product was poured into an ice-water mixture, filtered and washed multiple times, and then vacuum dried at 80°C to obtain carbonyl coal tar pitch material.

[0054] The second step, the preparation method of cobalt single-atom modified carbon nanosheets, is as follows:

[0055] Carbonyl coal tar material was dispersed in 40 mL of deionized water, and 0.1 g of cobalt nitrate hexahydrate was added. The mixture was heated to 60 °C and stirred for 12 h. The mixture was then filtered and washed several times with deionized water to obtain carbonyl coal tar adsorbed with cobalt ions. This cobalt-adsorbed carbonyl coal tar was dispersed in 50 mL of deionized water, and 0.3 g of boric acid was added. After stirring for 6 h, the mixture was dried in an 80 °C oven and ground in a mortar. Then, it was placed in a tube furnace and calcined at 800 °C for 2 h in an argon atmosphere at a heating rate of 5 °C / min to obtain cobalt single-atom modified carbon nanosheets, denoted as CoB-CNS. 800 .

[0056] Example 3

[0057] The first step, the preparation method of carbonyl coal tar pitch, is as follows:

[0058] 10 g of coal tar pitch was mixed with 300 mL of tetrahydrofuran for 12 h, and the insoluble matter was removed by centrifugation. Next, the soluble matter was heated at 80 °C with stirring to remove the tetrahydrofuran solvent. Then, 200 mL of 1,2-dichloroethane solution was added and stirred to dissolve the tetrahydrofuran soluble matter, forming mixture A. 20 g of anhydrous aluminum trichloride was placed in a three-necked flask, and 300 mL of 1,2-dichloroethane solution was added. After sonication for 1 h, magnetic stirring was continued for 4 h to form a viscous mixture. The three-necked flask containing the viscous mixture was placed in a water bath containing an ice-water mixture. When the temperature of the viscous mixture dropped to 0 °C, 50 g of oxaloyl chloride was added at a rate of drop per second. After the addition was complete, the reaction was continued with stirring for 1 h to form mixture B. In the water bath, the reaction mixture B was heated to 20 °C, and mixture A was slowly added. The reaction was continued with stirring for 12 h. Finally, the reaction product was poured into an ice-water mixture, filtered and washed multiple times, and then vacuum dried at 80°C to obtain carbonyl coal tar pitch material.

[0059] The second step, the preparation method of cobalt single-atom modified carbon nanosheets, is as follows:

[0060] Carbonyl coal tar pitch was dispersed in 40 mL of deionized water, and 0.1 g of cobalt nitrate hexahydrate was added. The mixture was heated to 60 °C and stirred for 12 h. The mixture was then filtered and washed several times with deionized water to obtain carbonyl coal tar pitch adsorbed with cobalt ions. This cobalt-adsorbed carbonyl coal tar pitch was dispersed in 50 mL of deionized water, and 5 g of urea was added. After stirring for 6 h, the mixture was dried in an 80 °C oven and ground in a mortar. Then, it was placed in a tube furnace and calcined at 800 °C for 2 h at a heating rate of 5 °C / min in an argon atmosphere to obtain cobalt single-atom modified carbon nanosheets, denoted as CoN-CNS. 800 .

[0061] Example 4

[0062] The first step, the preparation method of carbonyl coal tar pitch, is as follows:

[0063] 10 g of coal tar pitch was mixed with 300 mL of tetrahydrofuran for 12 h, and the insoluble matter was removed by centrifugation. Next, the soluble matter was heated at 80 °C with stirring to remove the tetrahydrofuran solvent. Then, 200 mL of 1,2-dichloroethane solution was added and stirred to dissolve the tetrahydrofuran soluble matter, forming mixture A. 20 g of anhydrous aluminum trichloride was placed in a three-necked flask, and 300 mL of 1,2-dichloroethane solution was added. After sonication for 1 h, magnetic stirring was continued for 4 h to form a viscous mixture. The three-necked flask containing the viscous mixture was placed in a water bath containing an ice-water mixture. When the temperature of the viscous mixture dropped to 0 °C, 50 g of oxaloyl chloride was added at a rate of drop per second. After the addition was complete, the reaction was continued with stirring for 1 h to form mixture B. In the water bath, the reaction mixture B was heated to 20 °C, and mixture A was slowly added. The reaction was continued with stirring for 12 h. Finally, the reaction product was poured into an ice-water mixture, filtered and washed multiple times, and then vacuum dried at 80°C to obtain carbonyl coal tar pitch material.

[0064] The second step, the preparation method of cobalt single-atom modified carbon nanosheets, is as follows:

[0065] Carbonyl coal tar material was dispersed in 40 mL of deionized water, and 0.1 g of cobalt nitrate hexahydrate was added. The mixture was heated to 60 °C and stirred for 12 h. The mixture was then filtered and washed several times with deionized water to obtain carbonyl coal tar adsorbed with cobalt ions. This was then placed in a tube furnace and calcined at 800 °C for 2 h in an argon atmosphere at a heating rate of 5 °C / min to obtain cobalt single-atom modified carbon nanosheets, denoted as Co-CNS. 800 .

[0066] Example 5

[0067] The first step, the preparation method of carbonyl coal tar pitch, is as follows:

[0068] 10 g of coal tar pitch was mixed with 300 mL of tetrahydrofuran for 12 h, and the insoluble matter was removed by centrifugation. Next, the soluble matter was heated at 80 °C with stirring to remove the tetrahydrofuran solvent. Then, 200 mL of 1,2-dichloroethane solution was added and stirred to dissolve the tetrahydrofuran soluble matter, forming mixture A. 20 g of anhydrous aluminum trichloride was placed in a three-necked flask, and 300 mL of 1,2-dichloroethane solution was added. After sonication for 1 h, magnetic stirring was continued for 4 h to form a viscous mixture. The three-necked flask containing the viscous mixture was placed in a water bath containing an ice-water mixture. When the temperature of the viscous mixture dropped to 0 °C, 50 g of oxaloyl chloride was added at a rate of drop per second. After the addition was complete, the reaction was continued with stirring for 1 h to form mixture B. In the water bath, the reaction mixture B was heated to 20 °C, and mixture A was slowly added. The reaction was continued with stirring for 12 h. Finally, the reaction product was poured into an ice-water mixture, filtered and washed multiple times, and then vacuum dried at 80°C to obtain carbonyl coal tar pitch material.

[0069] The second step, the preparation method of carbon nanosheets, is as follows:

[0070] Carbonyl coal tar pitch material was placed in a tube furnace and calcined at 800℃ for 2 h at a heating rate of 5 ℃ / min in an argon atmosphere to obtain carbon nanosheet material, denoted as CNS. 800 .

[0071] Comparative Example 1

[0072] The difference between this comparative example and Example 1 is that the calcination temperature in the second step is 700°C, while the other process conditions are the same as in Example 1.

[0073] Comparative Example 2

[0074] The difference between this comparative example and Example 1 is that the calcination temperature in the second step is 900°C, while the other process conditions are the same as in Example 1.

[0075] The XRD pattern of the prepared material is as follows: Figure 1 As shown in the test results, the materials obtained in Examples 1, 2, 3, 4, and 5 are all carbon materials, and there are no characteristic peaks of cobalt-related elements and compounds, indicating that cobalt exists in a single-atom form. From the SEM images ( Figure 2 As can be seen from the TEM images, the microstructures of Example 1, Comparative Example 1, and Comparative Example 2 are all two-dimensional ultrathin carbon nanosheet structures. Figure 3 It can be seen more clearly that the ultrathin carbon sheet structure and the carbon microcrystalline structure with wide interlayer spacing in Example 1, and no dispersed cobalt-related compound particles were observed on the surface. Figure 4 It can be seen that the material in Example 1 has a typical type IV adsorption-desorption curve, indicating that micropores and mesopores coexist in the material.

[0076] The materials obtained from Examples 1-5 and Comparative Examples 1-2 were used to assemble potassium-ion batteries to test their electrochemical performance.

[0077] The preparation method of potassium-ion batteries is as follows:

[0078] (1) Preparation of electrode sheets:

[0079] First, weigh 10 mg of polyvinylidene fluoride (PVDF) and place it in a grinding jar. Add 20 μL of N-methylpyrrolidone and stir for 3 minutes. Next, add 70 mg of carbon nanosheets and 20 mg of conductive carbon black to the grinding jar and continue grinding and mixing, adding an appropriate amount of N-methylpyrrolidone dropwise during the process until a homogeneous paste is formed. Then, transfer the paste to a container and cut it into 20*7.5 cm pieces. 2 A copper foil current collector is coated onto one end using a scraper to form a film. The coated copper foil is then placed in a vacuum drying oven and dried under vacuum at 90°C for 12 hours. After drying, it is cut into circular electrode sheets with a diameter of 13.14 mm using a manual slicer.

[0080] (2) Assembly of potassium-ion half-cells:

[0081] In an argon-filled glove box, the circular electrode sheet, diaphragm, and potassium metal sheet prepared in step (1) are assembled into a potassium ion half cell, and 100 μL of 0.8 M potassium hexafluorophosphate (KPF6) electrolyte is dropped onto the diaphragm.

[0082] Depend on Figure 6 It can be seen that Example 1 has good rate performance. When the current density is 0.05A / g, its specific capacity can reach 356.6 mAh / g, and when the current density is increased to 10A / g, its specific capacity is 74.2 mAh / g. Figure 6 It can be seen that the material obtained in Example 1 exhibits excellent cycling stability, maintaining a capacity retention of 87.5% after 1200 cycles at 2 A / g. Figure 6 , Figure 7 It can be seen that the rate capability and cycle performance of Example 1 are better than those of Examples 2-5 and Comparative Examples 1-2.

[0083] The above description is merely a preferred embodiment of the present invention and is illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A method for preparing cobalt single-atom modified carbon nanosheets, characterized in that, Includes the following steps: S1, carbonyl coal tar pitch is dispersed in deionized water, cobalt nitrate hexahydrate is added, the mixture is heated to 60°C and stirred for 12 hours, then the mixture is filtered and washed several times with deionized water to obtain carbonyl coal tar pitch@cobalt ions; S2, disperse the carbonyl coal tar pitch@cobalt ions obtained in step S1 in deionized water, add boric acid and urea, stir for 6 hours, and then dry the mixture in a forced-air drying oven at 80°C to obtain a solid mixture; S3. The solid mixture obtained in step S2 is placed in a tube furnace and carbonized at high temperature under an inert gas atmosphere to obtain cobalt single-atom modified carbon nanosheets.

2. The method for preparing cobalt single-atom modified carbon nanosheets as described in claim 1, characterized in that, In step S1, the preparation method of carbonyl coal tar pitch includes the following steps: S11, after stirring coal tar pitch and tetrahydrofuran solvent for 12 hours, the tetrahydrofuran insoluble matter is removed by centrifugation. The tetrahydrofuran soluble matter is removed by heating and stirring at 80°C to remove the tetrahydrofuran solvent. Then, 1,2-dichloroethane solution is added to dissolve the tetrahydrofuran soluble matter to obtain a mixed solution. S12, add 1,2-dichloroethane solution to anhydrous aluminum trichloride, sonicate for 1 hour, and then continue to stir magnetically for 4 hours to form a viscous mixture; S13, place the viscous mixture obtained in step S12 in an ice bath. When the temperature of the viscous mixture drops to 0°C, add oxaloyl chloride at a rate of 1 drop / s. After the addition is complete, continue stirring the reaction for 1 hour. S14, when the mixture after the reaction in step S13 is heated to 20°C, the mixed solution obtained in step S11 is slowly added and the mixture is stirred for 12 hours. S15, the reaction product from step S14 is poured into an ice-water mixture, filtered and washed multiple times, and finally dried under vacuum at 80°C to obtain carbonyl coal tar pitch.

3. The method for preparing cobalt single-atom modified carbon nanosheets as described in claim 2, characterized in that, In step S11, the mass of coal tar pitch used is 5-20g, the volume of tetrahydrofuran used is 150-500mL, and the volume of 1,2-dichloroethane solution used is 200-500mL.

4. The method for preparing cobalt single-atom modified carbon nanosheets as described in claim 2, characterized in that, In step S12, the mass of anhydrous aluminum trichloride used is 10-30g, the volume of 1,2-dichloroethane used is 100-400mL, and the mass of oxaloyl chloride used is 30-100g.

5. The method for preparing cobalt single-atom modified carbon nanosheets as described in claim 1, characterized in that, In step S1, the mass ratio of carbonyl coal tar pitch to cobalt nitrate hexahydrate is 1:0.02~0.

2.

6. The method for preparing cobalt single-atom modified carbon nanosheets as described in claim 1, characterized in that, In step S2, the mass ratio of carbonyl coal tar pitch @ cobalt ions, urea and boric acid is 1:3~8:0~0.

6.

7. The method for preparing cobalt single-atom modified carbon nanosheets as described in claim 1, characterized in that, In step S3, the inert gas is argon or nitrogen, the gas flow rate is 300 mL / min, the heating rate is 5 °C / min, the high-temperature carbonization temperature is 800 °C, and the time is 2 h.

8. A cobalt single-atom modified carbon nanosheet prepared by the preparation method according to any one of claims 1 to 7.

9. The application of cobalt single-atom modified carbon nanosheets as described in claim 8 in potassium-ion batteries.

10. The application of cobalt single-atom modified carbon nanosheets as described in claim 9 in potassium-ion batteries, characterized in that, The preparation of the potassium-ion battery includes the following steps: A1. Place polyvinylidene fluoride in a grinding jar, add nitrogen-methylpyrrolidone and stir. Then continue to add cobalt single-atom modified carbon nanosheets and conductive carbon black to the grinding jar, and continue grinding and mixing. During this process, nitrogen-methylpyrrolidone is added dropwise to form a uniform paste. A2. Transfer the slurry obtained in step A1 to one end of the cut copper foil current collector, scrape it into a film with a scraper, put the scraped copper foil into a vacuum drying oven, dry it under vacuum at 90°C for 12 hours, and cut it into a circular electrode sheet after drying. A3. Assemble the circular electrode sheet, separator, and potassium metal sheet prepared in step A2 into a potassium ion half cell, and drop 100 μL of 0.8 M potassium hexafluorophosphate electrolyte onto the separator.

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