Nanosheet self-assembled porous carbon sphere, preparation method, electrode and test method

Abstract

The invention discloses a nanosheet self-assembled porous carbon sphere, a preparation method, an electrode and a testing method, and the method comprises the following steps: mixing medium-temperature pitch with a Na2CO3 template agent and a K2CO3 activator in a certain proportion, and reacting in argon to obtain the nanosheet self-assembled porous carbon sphere. According to the method, Na2CO3 is adopted as a template agent, K2CO3 is adopted as an activating agent, K2CO3 reacts with medium-temperature pitch at a low temperature to generate K2O and CO2 gas, K2O directionally induces fat bonds between side chains and aromatic rings to break and recombine, and generated CO2 and other gas can further react with the medium-temperature pitch to form pore channels. Na2CO3 and K2CO3 form a molten state at a high temperature, on one hand, ions in the molten state promote molecular groups in a precursor to generate crosslinking, on the other hand, carbonate releases CO2 to continuously overflow to form rich micropores, and part of unmolten Na2CO3 serves as a template in a liquid phase environment and forms a mesoporous structure after being removed. And carrying out carbonization, enhanced polycondensation, activation and catalytic conversion to form the nanosheet self-assembled porous carbon spheres.

Description

Technical Field

[0001] The present invention relates to the field of carbon material and two-dimensional material preparation, and provides a nanoplate self-assembled porous carbon sphere, a preparation method, an electrode and a testing method. Background Art

[0002] Porous carbon is an important type of material that has developed rapidly in recent years. They have characteristics such as adjustable porous structure, stable physical and chemical properties, customizable specific surface area, and easy functionalization. Porous carbon materials have a wide range of applications in different scientific and technological fields, such as metallurgy and chemical engineering, water treatment, medical treatment, energy storage, etc. The preparation methods of porous carbon usually include physical / chemical activation methods, template methods, etc. The porous carbon materials prepared by these methods usually have a large specific surface area and a rich hierarchical porous structure. A supercapacitor is an energy storage device with the ability for high-power applications, and its electrode material is mainly porous carbon material. A high-quality supercapacitor porous carbon electrode not only requires a large specific surface area to provide an ion storage site, but also requires the material to provide excellent ion conduction characteristics and surface characteristics to enable the electrode material to exhibit better energy storage performance. Traditional porous carbon materials are blocky microscopically. Although the blocky porous carbon materials have rich pores inside, their weak surface ionophilic characteristics often inhibit the performance of the materials as supercapacitor electrode materials. Two-dimensional materials are a new type of material. Constructing a special microscopic morphology and adjusting the surface characteristics of the materials through customized methods is a feasible solution to improve the performance of supercapacitor porous carbon electrode materials. CN116375031A discloses a preparation method of a low-temperature activated activated carbon material, using a polymer as a precursor, and using benzoyl peroxide and cetyl dimethylethyl ammonium bromide as cross-linking agents to regulate the precursor, and obtaining the activated carbon material through low-temperature activation. This method uses chemical reagents as cross-linking agents, the treatment process is long, the process is not easy to control, and at the same time the chemical cross-linking agents are harmful to the environment and the human body, which is not conducive to industrial use. Summary of the Invention

[0003] The first object of the present invention is to provide a preparation method of a nanoplate self-assembled porous carbon sphere to alleviate the actual problems such as high production cost of porous carbon prepared by the prior art and low utilization rate of pores and surface as a supercapacitor electrode material.

[0004] The second object of the present invention is to provide a nanoplate self-assembled porous carbon sphere obtained by the above preparation method. The nanoplate self-assembled porous carbon sphere has the advantages of high electrical conductivity, high specific surface area and high surface utilization rate.

[0005] The technical solution is as follows:

[0006] A preparation method of nano-sheet self-assembled porous carbon spheres, which uses molten salt to enhance cross-linking polymerization to prepare nano-sheet self-assembled porous carbon spheres; characterized by including the following steps:

[0007] Step 1: Place medium-temperature pitch in a crusher for crushing to obtain powdered medium-temperature pitch;

[0008] Step 2: Take the crushed medium-temperature pitch and pulverize it in a jet mill, then perform classification screening to obtain medium-temperature pitch after fine screening;

[0009] Step 3: Uniformly mix the medium-temperature pitch after fine screening with Na2CO3 template agent and K2CO3 activator according to a mass ratio to obtain a mixed material;

[0010] Step 4: Place the mixed material in step 3 in a tubular furnace under an argon atmosphere, heat it to the cross-linking polymerization reaction temperature at a certain heating rate. This process requires rapid heating to enable sufficient cross-linking polymerization of the medium-temperature pitch. Subsequently, heat it to the activation temperature at a certain heating rate for the activation reaction, and then naturally cool it to room temperature and take it out;

[0011] Step 5: Use HCl solution to heat and stir the activated material to remove the remaining activator, and wash it with deionized water until the solution is neutral;

[0012] Step 6: Filter and dry the product obtained in step 5 to obtain the described nano-sheet self-assembled porous carbon spheres.

[0013] Preferably: The particle size of the powdered medium-temperature pitch in step 1 is below 30 μm. Medium-temperature pitch is originally a solid industrial product with relatively large particles. By crushing it into powder form, it lays a good foundation for subsequent jet milling and mixing operations.

[0014] Preferably: The particle size of the medium-temperature pitch after fine screening in step 2 is below 10 μm. The particle size of porous carbon materials not only affects the performance of the material itself but also affects the preparation of electrodes. Fine screening of medium-temperature pitch and targeted screening of particle size. Selecting particles below 10 μm can well control the particle size of nano-sheet self-assembled porous carbon spheres.

[0015] Preferably, the step 3 further includes that the mass ratio of the medium-temperature pitch after fine screening to the Na2CO3 template agent and the K2CO3 activator is 1:1 - 1:4, and the molar ratio of Na2CO3 to K2CO3 is 0:1 - 1:0. The Na2CO3 template agent acts as a solid template during the activation process, resulting in the generation of mesopores. The K2CO3 activator reacts with the pitch coke to decompose and produce K2O and CO2. Among them, K2O directionally induces the cleavage and recombination of the aliphatic bonds between the side chains and the aromatic rings. The generated gases such as CO2 will further react with the medium-temperature pitch to form pores. Na2CO3 and K2CO3 form a molten state at high temperature. On the one hand, the ions promote the cross-linking of the molecular groups in the precursor. On the other hand, the continuously overflowing CO2 released by the carbonate forms abundant micropores.

[0016] Preferably, the step 4 further includes: the enhanced cross-linking polymerization reaction temperature is 350°C - 450°C, the heating rate is 10°C / min, the cross-linking polymerization reaction time is 2 h, the activation temperature is 750°C - 950°C, the heating rate is 5°C / min, the activation reaction time is 2 - 5 h, and after the activation reaction is completed, it is naturally cooled to room temperature. The range of the polycondensation reaction temperature is 350°C - 450°C. Using a rapid heating rate of 10°C / min can cause severe polymerization and rearrangement of the molecular chains in the medium-temperature pitch. This rearrangement greatly affects the generation of the self-assembled porous carbon spheres of nanosheets realized by the subsequent activation reaction. The activation temperature is selected to be 750°C - 950°C. When the activation temperature is lower than 750°C, the effect of the activator is low and it cannot react with the medium-temperature pitch. When the activation temperature is higher than 950°C, the carbon chains in the medium-temperature pitch will undergo severe polymerization, resulting in a relatively high degree of crystallization of the porous carbon, which is not conducive to capacitive energy storage.

[0017] Preferably, in the step 5, the concentration of hydrochloric acid is 1 mol / L, and the stirring time is 5 - 8 hours. Dilute hydrochloric acid is used to pickle the porous carbon to remove impurities in the material. The purity of the porous carbon material greatly affects the performance of the material. By pickling and stirring for a long time, self-assembled porous carbon spheres of nanosheets with higher purity can be obtained.

[0018] Preferably, the product obtained in the step 6 is placed in an oven at 120°C and dried for 12 - 24 hours. Drying overnight is used to remove the moisture in the self-assembled porous carbon spheres of nanosheets and further improve the purity of the material.

[0019] The present invention discloses an electrode material for a supercapacitor, which is characterized in that the above-mentioned method of using molten salt to enhance the cross-linking polymerization effect is adopted to prepare self-assembled porous carbon spheres of nanosheets.

[0020] A supercapacitor, which is characterized in that it includes an electrode material, and the electrode material adopts the above-mentioned self-assembled porous carbon spheres of nanosheets.

[0021] Fabrication of the electrode. The prepared nanosheets, self-assembled porous carbon spheres, acetylene black, and polytetrafluoroethylene binder were mixed in a mass ratio of 8:1:1. Deionized water was added dropwise, and after mixing, it was pressed into a sheet and extruded onto nickel foam, and then placed in a vacuum drying oven at 120 °C and dried overnight.

[0022] The present invention adopts a test method for testing the electrochemical performance of the electrode, and this test method is the test method for testing the above-mentioned electrode; the electrochemical performance test of this electrode is carried out using a three-electrode system, with 6M KOH solution as the electrolyte, a platinum sheet electrode as the counter electrode, and a mercury oxide electrode as the reference electrode.

[0023] The present invention also discloses a nanosheet self-assembled porous carbon sphere, characterized in that the nanosheet self-assembled porous carbon sphere is prepared by the above method.

[0024] Preferably: the nanosheet self-assembled porous carbon sphere includes a large number of micropores and mesopores, the micropore pore size is distributed at 1.31 nm, and the mesopore pore size is 3.93 nm; at a current density of 1 A g -1 the discharge specific capacity in the aqueous alkaline electrolyte is 238 F g -1 .

[0025] Beneficial effects

[0026] 1. Using medium-temperature pitch as the raw material, a simple, green, low-temperature, and large-scale method is adopted to prepare nanosheet self-assembled porous carbon spheres.

[0027] 2. The preparation method of the nanosheet self-assembled porous carbon sphere provided by the present invention uses medium-temperature pitch as the preparation raw material, Na2CO3 as the template agent, and K2CO3 as the activator. At a lower temperature, K2CO3 reacts with medium-temperature pitch to generate gases such as K2O and CO2. Among them, K2O directionally induces the cleavage and recombination of the aliphatic bond between the side chain and the aromatic ring, and the generated CO2 and other gases will further react with medium-temperature pitch to form pores. At the same time, Na2CO3 and K2CO3 form a molten state at high temperature, and the liquid-phase rich ionic reaction environment is in full contact with the carbon-containing precursor. On the one hand, ions promote the cross-linking of molecular groups in the precursor, and on the other hand, the continuously overflowing CO2 released by the carbonate forms rich micropores. At the same time, part of the unmolten Na2CO3 acts as a template in the liquid-phase environment and forms a mesoporous structure after removal, thus preparing the nanosheet self-assembled porous carbon sphere.

[0028] 3. The nanosheet self-assembled porous carbon sphere has a relatively rich porous structure and a special microscopic morphology, which is beneficial to the storage of electrolyte ions and surface adsorption and desorption reactions; in the present invention, at a lower activation temperature, a nanosheet self-assembled porous carbon sphere with a high specific surface area, high conductivity, and high tap density can be obtained, which can be used as a supercapacitor electrode material and has very good capacitance performance. Description of the Drawings

[0029] Figure 1 Scanning electron microscope image of the nanosheet self-assembled porous carbon spheres prepared in Example 1.

[0030] Figure 2 Transmission electron microscope image of the nanosheet self-assembled porous carbon spheres prepared in Example 1.

[0031] Figure 3 Electrochemical performance image of the nanosheet self-assembled porous carbon spheres prepared in Example 1.

[0032] Figure 4 Isothermal adsorption line image of the nanosheet self-assembled porous carbon spheres prepared in Example 1.

[0033] Figure 5 Pore size distribution image of the nanosheet self-assembled porous carbon spheres prepared in Example 1. Detailed Description of the Invention

[0034] The following will describe the embodiments of the present invention in detail. However, those skilled in the art will understand that the following examples are only for the present invention and should not be regarded as limiting the scope of the present invention. The present invention will be further described below with reference to the accompanying drawings and examples.

[0035] A method for preparing nanosheet self-assembled porous carbon spheres, which uses molten salt to enhance the cross-linking polymerization to prepare nanosheet self-assembled porous carbon spheres; characterized by including the following steps:

[0036] Step 1: Place medium-temperature pitch in a crusher to crush it to obtain powdered medium-temperature pitch;

[0037] Step 2: Take the crushed medium-temperature pitch and pulverize it in a jet mill, and then perform classification screening to obtain medium-temperature pitch after fine screening;

[0038] Step 3: Uniformly mix the medium-temperature pitch after fine screening with Na2CO3 template agent and K2CO3 activator according to a mass ratio to obtain a mixed material;

[0039] Step 4: Place the mixed material in step 3 in a tube furnace under an argon atmosphere, and heat it to the cross-linking polymerization reaction temperature at a certain heating rate. This process requires rapid heating to cause sufficient cross-linking polymerization of the medium-temperature pitch, and then heat it to the activation temperature at a certain heating rate for the activation reaction, and naturally cool it to room temperature and then take it out;

[0040] Step 5: Use HCl solution to heat and stir the activated material to remove the remaining activator, and wash it with deionized water until the solution is neutral;

[0041] Step 6: Filter and dry the product obtained in Step 5 to obtain the nanosheet self-assembled porous carbon spheres.

[0042] Example 1

[0043] (1) Weigh 100 g of medium-temperature pitch and place it in a crusher for 15 min to obtain powdered medium-temperature pitch with a particle size of less than 30 μm.

[0044] (2) Take 50 g of the powdered medium-temperature pitch and place it in a jet mill for 15 min. After jet milling, the sample is sieved to obtain the medium-temperature pitch after fine sieving with a particle size of less than 10 μm.

[0045] (3) Uniformly mix the medium-temperature pitch after fine sieving with the Na2CO3 template agent and the K2CO3 activator in a mass ratio of 1:4, where the mass ratio of Na2CO3 to K2CO3 is 1.96:2.04. Take 10 g of the medium-temperature pitch after fine sieving, and take 19.6 g and 20.4 g of Na2CO3 and K2CO3 respectively.

[0046] (4) Place the mixed material under a tubular furnace in an argon atmosphere for enhanced cross-linking and activation. The enhanced cross-linking temperature is 450 °C, the cross-linking time is 2 h, the activation temperature is 920 °C, and the activation time is 5 h. The heating rate is 5 °C / min. After activation, it is naturally cooled to room temperature.

[0047] (5) Wash the activated material with 1 mol / L HCl solution and deionized water until the solution is neutral. Finally, place it in a freeze dryer and freeze-dry for 12 h to obtain the nanosheet self-assembled porous carbon spheres.

[0048] (6) Fabrication of the electrode. Mix the prepared nanosheet self-assembled porous carbon spheres, acetylene black, and polytetrafluoroethylene binder in a mass ratio of 8:1:1, add deionized water and mix, then press it into a sheet and extrude it onto nickel foam, and place it in a vacuum drying oven at 120 °C and dry overnight.

[0049] (7) The electrochemical performance test of the obtained electrode is carried out using a three-electrode system. 6 M KOH solution is used as the electrolyte, a platinum sheet is used as the counter electrode, and a mercury oxide electrode is used as the reference electrode. A CH Instrument electrochemical workstation is used for cyclic voltammetry testing, impedance testing, and galvanostatic charge-discharge performance testing. For cyclic voltammetry testing, the voltage range is -1 V to 0 V, and the scan rate is 10 mV s 1 ; for impedance testing, the frequency range is 100 KHz - 0.01 Hz, and the voltage is the initial open-circuit voltage; for galvanostatic charge-discharge performance testing, the voltage range is -1 V to 0 V, and the current density is selected as 1 A g -1 .

[0050] The nanosheet self-assembled porous carbon spheres obtained through Example 1 are shown in the attached drawings, where,Figure 1 For the scanning electron microscope after activation, it can be seen that the prepared material is a microsphere structure stacked by two-dimensional nanosheets.

[0051] Figure 2 For the transmission electron microscope image after activation, it can be clearly seen that the prepared material is assembled by two-dimensional nanosheets, and there are some microporous structures attached to the nanosheets.

[0052] Figure 3 The following shows the three-electrode galvanostatic charge-discharge curve of the self-assembled porous carbon spheres of the prepared nanosheets. At a current density of 1 A g -1 , the material exhibits a high discharge specific capacity of 238 F g -1 .

[0053] Figure 4 The following shows the isothermal adsorption curve of the self-assembled porous carbon spheres of the prepared nanosheets. The isothermal adsorption and desorption test results show that the specific surface area of this material is 1560 m 2 g -1 . It can be seen from the figure that the sample has a type-IV isothermal curve, indicating that there are a large number of micropores and mesopores in the sample, proving that this material is a porous structure.

[0054] Figure 5 The following shows the pore size distribution diagram of the prepared self-assembled porous carbon spheres of the nanosheets. The pore size distribution results show that the micropore size of this material is mainly distributed at 1.31 nm, while the mesopore size is at 3.93 nm.

[0055] Example 2

[0056] (1) Weigh 100 g of medium-temperature pitch and place it in a crusher for crushing for 15 min to obtain powdered medium-temperature pitch, with a particle size of less than 30 μm.

[0057] (2) Take 50 g of the powdered medium-temperature pitch and place it in a jet mill. The crushing time is 15 min. The sample after jet milling is sieved to obtain the medium-temperature pitch after fine sieving, with a particle size of less than 10 μm.

[0058] (3) Uniformly mix the medium-temperature pitch after fine sieving with the Na2CO3 template agent and the K2CO3 activator in a mass ratio of 1:4. The mass ratio of Na2CO3 to K2CO3 is 1.96:2.04. Take 10 g of the medium-temperature pitch after fine sieving, and take 19.6 g and 20.4 g of Na2CO3 and K2CO3 respectively.

[0059] (4) Place the mixed material under an argon atmosphere in a tube furnace for enhanced cross-linking and activation. The enhanced cross-linking temperature is 450 °C, the cross-linking time is 5 h, the activation temperature is 920 °C, and the activation time is 5 h. The heating rate is 5 °C / min. After activation, it is naturally cooled to room temperature.

[0060] (5) The activated material was washed with 1 mol / L HCl solution and deionized water until the solution became neutral. Finally, it was placed in a freeze dryer and freeze-dried for 12 h to obtain nanoflake self-assembled porous carbon spheres.

[0061] Analysis of the nanoflake self-assembled porous carbon spheres obtained from the above examples shows that if the crosslinking time is too long, the polycondensation between molecular chains is too severe, which is not conducive to the subsequent activation pore-forming process and results in a smaller specific surface area.

[0062] Example 3

[0063] (1) Weigh 100 g of medium-temperature pitch and place it in a crusher for 15 min to obtain powdered medium-temperature pitch with a particle size of less than 30 μm.

[0064] (2) Take 50 g of the powdered medium-temperature pitch and place it in a jet mill for 15 min. The sample after jet milling is sieved to obtain medium-temperature pitch after fine sieving with a particle size of less than 10 μm.

[0065] (3) The medium-temperature pitch after fine sieving was evenly mixed with Na2CO3 template agent and K2CO3 activator in a mass ratio of 1:4, where the mass ratio of Na2CO3 and K2CO3 was 1.96:2.04. 10 g of the medium-temperature pitch after fine sieving was taken, and 19.6 g and 20.4 g of Na2CO3 and K2CO3 were taken respectively.

[0066] (4) The mixed material was placed under an argon atmosphere in a tubular furnace for enhanced crosslinking and activation. The enhanced crosslinking temperature was 450 °C, the crosslinking time was 0 h, the activation temperature was 920 °C, and the activation time was 5 h. The heating rate was 5 °C / min. After activation, it was naturally cooled to room temperature.

[0067] (5) The activated material was washed with 1 mol / L HCl solution and deionized water until the solution became neutral. Finally, it was placed in a freeze dryer and freeze-dried for 12 h to obtain nanoflake self-assembled porous carbon spheres.

[0068] Analysis of the nanoflake self-assembled porous carbon spheres obtained from the above examples shows that the molecular groups of the medium-temperature pitch without enhanced crosslinking reaction did not produce directional recombination and arrangement, and the structure of nanoflake self-assembled porous carbon spheres could not be obtained.

[0069] Example 4

[0070] (1) Weigh 100 g of medium-temperature pitch and place it in a crusher for 15 min to obtain powdered medium-temperature pitch with a particle size of less than 30 μm.

[0071] (2) Take 50 g of powdered medium-temperature pitch and place it in a jet mill. The pulverization time is 15 min. The sample after jet milling is sieved to obtain the medium-temperature pitch after fine sieving, with a particle size of less than 10 μm.

[0072] (3) Uniformly mix the medium-temperature pitch after fine sieving and the K2CO3 activator in a mass ratio of 1:4. Take 10 g of the medium-temperature pitch after fine sieving and 40 g of K2CO3.

[0073] (4) Place the mixed material under a tubular furnace in an argon atmosphere for enhanced cross-linking and activation. The enhanced cross-linking temperature is 450 °C, the cross-linking time is 2 h, the activation temperature is 920 °C, and the activation time is 5 h. The heating rate is 5 °C / min. After activation, it is naturally cooled to room temperature.

[0074] (5) Wash the activated material with 1 mol / L HCl solution and deionized water until the solution becomes neutral. Finally, place it in a freeze dryer and freeze-dry for 12 h to obtain nanosheet self-assembled porous carbon spheres.

[0075] It can be seen through analysis of the nanosheet self-assembled porous carbon spheres obtained from the above examples that when using potassium carbonate alone as the activator, too much potassium carbonate decomposes during the enhanced cross-linking reaction, resulting in an increase in the weak intermolecular forces and preventing the nanosheets from self-assembling into spheres.

[0076] Example 5

[0077] (1) Weigh 100 g of medium-temperature pitch and place it in a crusher for 15 min to obtain powdered medium-temperature pitch with a particle size of less than 30 μm.

[0078] (2) Take 50 g of powdered medium-temperature pitch and place it in a jet mill. The pulverization time is 15 min. The sample after jet milling is sieved to obtain the medium-temperature pitch after fine sieving, with a particle size of less than 10 μm.

[0079] (3) Uniformly mix the medium-temperature pitch after fine sieving and the Na2CO3 template in a mass ratio of 1:4. Take 10 g of the medium-temperature pitch after fine sieving and 40 g of Na2CO3.

[0080] (4) Place the mixed material under a tubular furnace in an argon atmosphere for enhanced cross-linking and activation. The enhanced cross-linking temperature is 450 °C, the cross-linking time is 2 h, the activation temperature is 920 °C, and the activation time is 5 h. The heating rate is 5 °C / min. After activation, it is naturally cooled to room temperature.

[0081] (5) Wash the activated material with 1 mol / L HCl solution and deionized water until the solution becomes neutral. Finally, place it in a freeze dryer and freeze-dry for 12 h to obtain nanosheet self-assembled porous carbon spheres.

[0082] Through the analysis of the nanosheet self-assembled porous carbon spheres obtained from the above embodiments, it can be known that when using only sodium carbonate for activation, a two-dimensional nanosheet structure cannot be formed. Although the material has more mesoporous channels, its specific surface area is small and its capacitance performance is poor.

[0083] The nanosheet self-assembled porous carbon spheres obtained in Test Examples 1-5 were tested, and the specific data are shown in Table 1: Table 1

[0084]

[0085] As can be seen from Table 1, by using the method provided by the present invention to prepare nanosheet self-assembled porous carbon spheres with molten salt enhanced cross-linking polymerization, nanosheet self-assembled porous carbon spheres with a high specific surface area, high tap density and special morphology can be obtained. The nanosheet self-assembled porous carbon spheres obtained by the scheme of Example 1 have a relatively high specific surface area and a large tap density, and have more excellent capacitance performance as supercapacitor carbon.

[0086] The preparation method of a nanosheet self-assembled porous carbon sphere provided by the present invention has been introduced in detail above. By introducing a method of enhancing cross-linking polymerization, potassium carbonate is used as a mild agent to enhance the cross-linking polymerization between asphalt molecular groups at a lower temperature, and the influence of the activator on asphalt molecular groups is optimized. And by adding sodium carbonate, the chemical reaction of potassium carbonate on the carbon precursor is neutralized to form a liquid phase environment of molten salt, which not only controls the transformation of the morphology but also controls the development of the pores.

[0087] Finally, it should be noted that the above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection required by the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of nanosheet self-assembled porous carbon spheres, which uses molten salt to enhance cross-linking polymerization to prepare nanosheet self-assembled porous carbon spheres; characterized in that, It includes the following steps: Step 1: Place medium-temperature pitch in a crusher for crushing to obtain powdered medium-temperature pitch; Step 2: Take the crushed medium-temperature pitch and pulverize it in a jet mill, then perform classification screening to obtain medium-temperature pitch after fine screening; Step 3: Uniformly mix the medium-temperature pitch after fine screening with a Na2CO3 template agent and a K2CO3 activator according to a mass ratio to obtain a mixed material; Step 4: Place the mixed material in Step 3 in a tubular furnace under an argon atmosphere and heat it to the cross-linking polymerization reaction temperature at a certain heating rate. This process requires rapid heating to enable sufficient cross-linking polymerization of the medium-temperature pitch. Subsequently, heat it to the activation temperature at a certain heating rate for the activation reaction, and then naturally cool it to room temperature before taking it out; Step 5: Heat and stir the activated material with an HCl solution to remove the remaining activator, and wash it with deionized water until the solution is neutral; Step 6: Filter and dry the product obtained in Step 5 to obtain the self-assembled porous carbon spheres of nanosheets.

2. The preparation method of the nanosheet self-assembled porous carbon spheres according to claim 1, characterized in that: In Step 1, the particle size of the powdered medium-temperature pitch is below 30 μm; in Step 2, the particle size of the medium-temperature pitch after fine screening is below 10 μm.

3. The preparation method of the nanosheet self-assembled porous carbon spheres according to claim 1, characterized in that: Step 3 further includes: The mass ratio of the medium-temperature pitch after fine screening to the Na2CO3 template agent and the K2CO3 activator is 1∶1 - 1∶4, wherein the molar ratio of Na2CO3 and K2CO3 is 0∶1 - 1∶0.

4. The preparation method of the nanosheet self-assembled porous carbon spheres according to claim 1, characterized in that: Step 4 further includes: The cross-linking polymerization reaction temperature is 350°C - 450°C, the heating rate is 10°C / min, the reaction time is 2 h, the activation reaction temperature is 750°C - 950°C, the heating rate is 5°C / min, the activation reaction time is 2 - 5 h, and after the activation reaction is completed, it is naturally cooled to room temperature.

5. The preparation method of the nanosheet self-assembled porous carbon spheres according to claim 1, characterized in that: In Step 5, the concentration of hydrochloric acid is 1 mol / L, and the stirring time is 5 - 8 hours.

6. The preparation method of the nanosheet self-assembled porous carbon spheres according to claim 1, characterized in that: The product obtained in Step 6 is placed in an oven and dried for 12 - 24 hours.

7. A nanoplate self-assembled porous carbon sphere, characterized in that, The self-assembled porous carbon spheres of nanosheets are prepared by using the preparation method of the self-assembled porous carbon spheres of nanosheets according to any one of claims 1 - 6.

8. The nanoplate self-assembled porous carbon spheres according to claim 7, characterized in that: The self-assembled porous carbon nanospheres include a large number of micropores and mesopores. The micropore aperture is distributed at 1.31 nm, and the mesopore aperture is at 3.93 nm. At a current density of 1 A g -1 , the discharge specific capacity in an aqueous alkaline electrolyte is 238 F g -1 .

9. An electrode; characterized in that: Mix the self-assembled porous carbon spheres of nanosheets described in claim 7 with acetylene black and a polytetrafluoroethylene binder in a mass ratio of 8∶1∶1, add deionized water and mix, then press it into a sheet and extrude it onto nickel foam, and place it in a vacuum drying oven at 120°C and dry it overnight.

10. The test method for testing the electrochemical performance of an electrode. This test method is used to test the electrode described in claim 9; this test for the electrochemical performance of the electrode is carried out using a three-electrode system, with a 6M KOH solution as the electrolyte, a platinum sheet electrode as the counter electrode, and a mercury oxide electrode as the reference electrode.

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