Screened carbon, and preparation method therefor and use thereof

Abstract

Disclosed in the present invention are screened carbon, and a preparation method therefor and a use thereof. Carbon is primarily deposited at pore openings of the screened carbon; carbon is secondarily deposited at the positions, corresponding to the pore openings, on the surface of the primary deposited carbon; the carbon deposited two times do not enter the interior of pore bodies; the diameters of the pores subjected to two-time deposition are all less than 0.33 nm; the specific surface area of the screened carbon subjected to a CO2 adsorption and desorption test is 0-10 m2 / g. By means of two chemical vapor deposition, the present invention adjusts the pore openings to be less than 0.33 nm while keeping the original sizes of the pore bodies, thereby effectively improving the initial coulombic efficiency of a carbon material.

Description

A screening carbon and its preparation method and application Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to screening carbon and a preparation method and application thereof. Background Art

[0002] Amorphous carbon materials are the most commercially promising battery negative electrode materials due to their low cost, low operating potential and excellent cycle stability. However, amorphous carbon materials currently face the problem of low first coulombic efficiency, which seriously hinders their commercialization process.

[0003] The electrochemical properties of amorphous carbon materials are closely related to their microstructure, especially the pore structure of carbon materials, which directly affects their first coulombic efficiency. The Chinese patent application "High-energy and high-power carbon materials and preparation methods and sodium-ion batteries" with publication number CN116553547A discloses a high-energy and high-power carbon material with a pore diameter of 0.1-0.4nm. However, the pore diameter of 0.4nm is still too large, which is not conducive to the first coulombic efficiency, and the pore size needs to be further controlled.

[0004] The present invention discloses a screening carbon, a preparation method and an application thereof. The pore size of the screening carbon can be adjusted twice to be lower than 0.33 nm, and there is no pore size between 0.33 nm and 0.4 nm. The first coulombic efficiency of the screening carbon is significantly improved.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide a screening type carbon to solve the problem of excessively large pore size of carbon materials in the prior art.

[0007] Another object of the present invention is to provide a method for preparing the screening carbon.

[0008] Another object of the present invention is to provide application of the sieve-type carbon in battery electrodes.

[0009] The technical solution adopted to achieve the purpose of the present invention is:

[0010] A screening carbon, wherein the pore opening and the periphery of the pore opening are deposited with primary deposited carbon, the surface of the primary deposited carbon is deposited with secondary deposited carbon at the position of the pore opening, the two deposited carbons do not enter the pore belly, the pore opening diameter after the two depositions is less than 0.33nm, and the specific surface area of ​​the screening carbon after CO2 adsorption and desorption test is 0-10m 2 / g.

[0011] In the above technical solution, the pore diameter of the screening carbon is 0.5-10nm.

[0012] Another aspect of the present invention is a method for preparing screening carbon, comprising the following steps:

[0013] Step 1: First chemical vapor deposition to quickly reduce the pore size: Place the porous carbon in a chemical vapor deposition device, introduce a predetermined flow of protective gas, raise the temperature to 1100-1300°C, then introduce a predetermined flow of the first carbon source gas, and perform the first heat preservation;

[0014] Step 2, second chemical vapor deposition to refine the orifice to a diameter of less than 0.33 nm: After the first heat preservation, the first carbon source gas is cut off, the temperature is lowered to 600-800°C, and the second carbon source gas at a predetermined flow rate is introduced, and the second heat preservation is performed;

[0015] Step 3: Turn off the second carbon source gas and cool the temperature to room temperature at a predetermined cooling rate to obtain the screening carbon.

[0016] As shown in Figure 17, the temperature of the first chemical vapor deposition (rapidly shrinking the orifice) is 1100-1300°C. At this temperature, the carbon source gas is rapidly cracked and deposited, sacrificing the selectivity of the carbon source gas deposition at the orifice (partial deposition occurs outside the pore), and the orifice is quickly reduced. The orifice is a defect site, and the rapidly cracked carbon source gas is mainly deposited at the orifice position, with a small amount of deposition outside the pore. If the temperature is lower than 1100°C, the purpose of rapidly reducing the orifice cannot be achieved, and the orifice reduction rate is slow, causing the deposited carbon to enter the pore; if the temperature is higher than 1300°C, the deposition rate is too fast, and the orifice may be sealed instantly, resulting in excessive ineffective carbon deposits.

[0017] The second chemical vapor deposition (refining the pore to a diameter of less than 0.33nm) is performed at a temperature of 600-800°C. At this temperature, the carbon source gas decomposes slowly, selectively depositing at the pore mouth and preventing deposition outside the pore, further refining the pore size to less than 0.33nm. If the temperature is higher than 800°C, the refinement goal cannot be achieved, resulting in excessive carbon deposition outside the pore. If the temperature is lower than 600°C, the carbon source gas cannot decompose and deposit.

[0018] In the above technical solution, the porous carbon in step 1 is walnut shell-based porous carbon, bamboo-based activated carbon, coconut shell-based porous carbon, peanut shell-based porous carbon, petroleum coke-based porous carbon, needle coke-based porous carbon or activated carbon fiber.

[0019] In the above technical solution, the first carbon source gas in step 1 is methane, benzene vapor, toluene vapor, xylene vapor, ethane, propane or acetylene;

[0020] The second carbon source gas in step 2 is methane, benzene vapor, toluene vapor, xylene vapor, ethane, propane or acetylene; preferably, the first carbon source gas is the same as the second carbon source gas.

[0021] In the above technical solution, the flow rate of the first carbon source gas in step 1 is 10-500 ml / min. If the flow rate of the carbon source gas is too small, the orifice size left during the first chemical vapor deposition will be larger, which will cause a large amount of deposited carbon to enter the pore during the second step of fine-tuning the orifice; if the flow rate of the carbon source gas is too large, the pore will be excessively blocked, and a large amount of invalid deposited carbon will be generated at the orifice, resulting in too low an initial coulombic efficiency during sodium storage.

[0022] In the above technical solution, the first insulation time in step 1 is 0-30 minutes and is not 0; the purpose of the first chemical vapor deposition is to quickly reduce the pore opening to prevent the deposited carbon from entering the pore. If the insulation time is too long, it will cause excessive deposition and affect the first coulombic efficiency of sodium storage.

[0023] In the above technical solution, after completing step 1, the size of the orifice can be adjusted to the point where N2 cannot enter but CO2 can enter most of the orifices, that is, the specific surface area of ​​the N2 adsorption and desorption test is 0-100m 2 / g, the specific surface area of ​​CO2 adsorption and desorption test is 100-2000m 2 / g, and the diameter of most pores is 0.33-0.364 nm.

[0024] In the above technical solution, the flow rate of the second carbon source gas in step 2 is ≥10 ml / min. If the flow rate of the carbon source gas is too small, it will take a long time to fine-tune the orifice.

[0025] In the above technical solution, the second holding time in step 2 is ≥3h. Since the deposition temperature is controlled within a relatively low range in the second stage of deposition, deposition occurs selectively only at the pore opening. After the pore opening is refined, deposition will not occur. If the deposition time is less than 3h, the pore opening cannot be refined, resulting in a lower initial coulombic efficiency and a lower sodium storage capacity. Step 2 is controlled at a relatively low reaction temperature. The carbon source gas cracking and deposition must occur at locations with low energy barriers. For porous carbon, the sites with low energy barriers are defect-rich pore openings. When the pore openings are fully occupied by deposited carbon, there are no sites for carbon source gas cracking and deposition, so no deposition will occur even if the time is extended.

[0026] In the above technical solution, after the orifice is refined in step 2, the orifice size of all the holes is closed to the point where CO2 cannot enter, that is, the specific surface area of ​​the CO2 adsorption and desorption test is 0-10m 2 / g, at this time the pore diameters of all pores are less than 0.33nm.

[0027] In the above technical solution, the pore size of the sieve-type carbon obtained in step 3 is consistent with the pore size of the porous carbon in step 1.

[0028] In the above technical solution, the cooling rate in step 3 is 5-20°C / min.

[0029] Another aspect of the present invention also includes the use of the sieve-type carbon in a battery negative electrode.

[0030] In the above technical solution, the sodium storage capacity of the battery negative electrode is 350-600 mAh / g, and the first coulombic efficiency is 91-95%.

[0031] Another aspect of the present invention also includes a negative electrode based on sieved carbon, which includes a negative electrode active material, a conductive agent and a binder, wherein the negative electrode active material is the sieved carbon; the conductive agent is SUPER-P, KS-6, conductive graphite, carbon nanotubes, graphene, carbon fiber VGCF, acetylene black or Ketjen black; and the binder is PVDF, CMC, SBR, PTFE, SA, PAA or PAN.

[0032] Another aspect of the present invention also includes a battery comprising a positive electrode, the negative electrode based on sieve-type carbon, and an electrolyte;

[0033] The active material of the positive electrode is a transition metal layered oxide, a sodium polyanion compound, Prussian blue or Prussian white.

[0034] The electrolyte includes an organic solvent and a sodium salt, wherein the organic solvent includes EC, PC, DMC, DEC, EMC, EA, FEC or VC; and the sodium salt includes NaClO4, NaPF6, NaBF4, NaFSI or NaTFSI.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The present invention utilizes two chemical vapor depositions with stepped temperatures to prepare screening carbon. In step 1, the first chemical vapor deposition rapidly blocks the pores at high temperatures (1100-1300°C) to prevent deposited carbon from entering the pore belly, and rapidly shrinks the pore opening to a smaller size at a relatively fast rate. The rapid shrinkage of the pore opening actually sacrifices the selectivity of the deposition reaction at the pore opening, while enhancing the efficiency of the pore blocking. At this time, deposited carbon will appear around the pore opening. In step 2, the second chemical vapor deposition refines the pore opening at low temperatures (600-800°C) to a diameter of less than 0.33 nm. Since the pore opening has reached a smaller range after completing step 1, the second chemical vapor deposition carbon can be inhibited from entering the pore. Moreover, the deposition at low temperatures in step 2 is selective deposition that occurs only at the pore opening, and no further deposited carbon will be generated outside the pore.

[0037] 2. The present invention uses two chemical vapor depositions to adjust the pore diameter to less than 0.33 nm while maintaining the original pore size (during the two-step deposition process, the deposited carbon will not enter the interior of the pore), effectively improving the first coulombic efficiency of the carbon material, which is conducive to the commercial application of screening carbon materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG1 shows a small-angle X-ray scattering diagram of Example 1.

[0039] FIG2 shows a nitrogen adsorption-desorption test diagram of Example 1.

[0040] FIG3 shows a carbon dioxide adsorption and desorption test diagram of Example 1.

[0041] FIG4 shows TEM images of Example 1 before and after the first chemical vapor deposition.

[0042] FIG5 shows a correlation curve between reaction time and weight gain during the second chemical vapor deposition process of Example 1.

[0043] FIG6 shows TEM images of the porous carbon of Example 1 and the screening-type carbon obtained in Example 1. ...

[0044] FIG7 shows the first cycle charge and discharge curve of the negative electrode of the sodium ion battery of Example 1.

[0045] FIG8 shows a small-angle X-ray scattering diagram of Comparative Example 1.

[0046] FIG9 shows a nitrogen adsorption-desorption test diagram of Comparative Example 1.

[0047] FIG10 shows a carbon dioxide adsorption and desorption test diagram of Comparative Example 1.

[0048] FIG11 shows a TEM image of the carbon material of Comparative Example 1.

[0049] FIG12 shows the first cycle charge and discharge curve of the negative electrode of the sodium ion battery of Comparative Example 1.

[0050] FIG13 shows a small-angle X-ray scattering diagram of Comparative Example 2.

[0051] FIG14 shows a carbon dioxide adsorption and desorption test diagram of Comparative Example 2.

[0052] FIG15 shows a TEM image of the carbon material of Comparative Example 2.

[0053] FIG16 shows the first cycle charge and discharge curve of the negative electrode of the sodium ion battery of Comparative Example 2.

[0054] FIG. 17 is a schematic diagram of a two-step chemical vapor deposition process according to the present invention. DETAILED DESCRIPTION

[0055] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0056] Example 1

[0057] A method for preparing screening carbon comprises the following steps:

[0058] Step 1: First chemical vapor deposition to quickly reduce the pore size: Place porous carbon with rich pore structure into a tube furnace. The porous carbon is activated carbon fiber, and the small angle scattering test specific surface area is 1420m 2 / g, the specific surface area of ​​nitrogen adsorption and desorption test is 1380m 2 / g, the porous carbon has a large specific surface area, indicating that it has a rich number of pores and a large internal space, so it is a large pore belly raw material, and then a protective gas argon gas with a flow rate of 90 ml / min is introduced, and the temperature is increased to a final temperature of 1200°C at a heating rate of 10°C / min. Under the final temperature condition of 1200°C, methane gas with a flow rate of 30 ml / min is introduced, and the reaction is continued for 25 minutes to quickly reduce the pore opening; step 2, the second chemical vapor deposition is used to refine the pore opening to a diameter of less than 0.33 nm: the methane gas is cut off, the temperature is lowered to 700°C, and methane gas with a flow rate of 10 ml / min is introduced, and the reaction is continued for 300 minutes, and the pore opening is further refined to a diameter of less than 0.33 nm;

[0059] Step 3, turning off the carbon source gas and cooling the temperature to room temperature at a cooling rate of 10°C / min to obtain the screening carbon.

[0060] As shown in Figure 1, the specific surface area of ​​the porous carbon in step 1 was measured by small-angle X-ray scattering to be 1420 m 2 / g, the specific surface area of ​​the sieved carbon obtained in step 3 was measured by small-angle X-ray scattering to be 1415m 2 / g, indicating that the deposited carbon in the two chemical vapor deposition phases did not enter the pore belly, achieving the effect of selectively adjusting the pore opening.

[0061] As shown in Figure 2, the specific surface area of ​​the porous carbon measured by nitrogen adsorption and desorption in step 1 is 1380 m 2 / g, after the first chemical vapor deposition in step 1, the specific surface area is reduced to 30m 2 / g, after the second chemical vapor deposition in step 2, the specific surface area is reduced to 5m 2 / g, indicating that after the first chemical vapor deposition, the pore diameters of most pores are smaller than 0.364 nm (the molecular dynamics diameter of N2), and after the second chemical vapor deposition, the pore diameters of all pores are smaller than 0.364 nm.

[0062] As shown in Figure 3, the specific surface area of ​​the porous carbon measured by carbon dioxide adsorption and desorption in step 1 is 1358m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 600m 2 / g, after the second chemical vapor deposition, the specific surface area dropped to 6m 2 / g, indicating that after the rapid reduction of the pore size in step 1, the pore diameters of most pores are still larger than 0.330nm (the molecular dynamics diameter of CO2). After the fine pore size in step 2, the pore diameters of all pores are less than 0.330nm.

[0063] During the first chemical vapor deposition, the rapidly cracked carbon source gas is mainly deposited at the pore mouth, with a small amount of deposition outside the pore. As shown in Figure 4, the porous carbon surface does not change much before and after the first chemical vapor deposition, indicating that there is not much carbon deposition outside the pore.

[0064] During the second chemical vapor deposition, the carbon source gas cracking rate is slow, and it is selectively deposited at the pore mouth, and no deposition occurs outside the pore. As shown in Figure 5, when the weight of the deposited carbon in the secondary deposition reaches the point where the pore mouth is blocked to less than 0.33nm, the weight gain will not increase no matter how long the reaction time is extended, indicating that the deposition reaction can only occur at the pore mouth.

[0065] As shown in Figure 6, before and after the two chemical vapor deposition processes, the internal structure of the pores did not change, and the deposited carbon did not enter the pores, indicating a selective effect.

[0066] The negative electrode of the battery is prepared by using the screening method as follows:

[0067] The sieved carbon was used as the negative electrode active material, and polyvinylidene fluoride (PVDF) was used as a binder. The mixture was evenly mixed with the conductive agent acetylene black in a mass ratio of 90:5:5 in NMP (N-methylpyrrolidone) solvent, coated into an electrode film, and dried in a vacuum drying oven at 120°C for 12 hours. The sieved carbon negative electrode sheet was obtained by rolling and punching. A metal sodium sheet was used as the counter electrode, and 1 mol / L NaPF6 (EC:DEC=1:1) was used as the electrolyte. The sieved carbon negative electrode sheets obtained above were assembled into 2032 button batteries in a glove box to test their electrochemical properties.

[0068] As shown in FIG7 , it can be seen that the sodium ion battery negative electrode prepared in this embodiment has a first coulombic efficiency of up to 93%, a reversible specific capacity of up to 354 mAh / g, and a low potential platform specific capacity of 280 mAh / g.

[0069] Example 2

[0070] A method for preparing screening carbon comprises the following steps:

[0071] Step 1: First chemical vapor deposition to quickly shrink the pore: porous carbon (walnut shell-based porous carbon, small angle scattering test specific surface area is 802m 2 / g, and the specific surface area of ​​nitrogen adsorption and desorption test is 798m 2 / g, small pore belly raw material) was placed in a tube furnace, and a protective gas argon gas was introduced at a flow rate of 90ml / min. The temperature was raised at a heating rate of 10℃ / min to a final temperature of 1200℃. At the final temperature of 1200℃, methane gas was introduced at a flow rate of 30ml / min and the reaction was continued for 25min to rapidly reduce the pore size.

[0072] Step 2: Second chemical vapor deposition to refine the pores to a diameter of less than 0.33 nm: cut off the methane gas, cool to 700 degrees, introduce methane gas at a flow rate of 10 ml / min, and continue the reaction for 300 minutes. The pore entrances are further refined to a diameter of less than 0.33 nm.

[0073] Step 3, turning off the carbon source gas and cooling the temperature to room temperature at a cooling rate of 10°C / min to obtain the screening carbon.

[0074] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by small-angle X-ray scattering to be 802 m 2 / g, the specific surface area of ​​the sieved carbon obtained in step 3 was measured by small angle X-ray scattering to be 800m 2 / g, indicating that the deposited carbon from the two chemical vapor deposition phases did not enter the pore belly, achieving the effect of selectively adjusting the pore opening.

[0075] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by nitrogen adsorption and desorption to be 798 m 2 / g, after the first chemical vapor deposition, the specific surface area is reduced to 15m 2 / g, after the second chemical vapor deposition, the specific surface area is reduced to 5m 2 / g, indicating that after the first chemical vapor deposition, the pore diameters of most pores are smaller than 0.364nm (the molecular dynamics diameter of N2). After the second chemical vapor deposition, i.e., pore refinement, the pore diameters of all pores are smaller than 0.364nm.

[0076] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was 780 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 310m 2 / g, after the second chemical vapor deposition, the specific surface area dropped to 3m 2 / g, indicating that after the pores are rapidly reduced in step 1, the diameters of most pores are still larger than 0.330 nm (the molecular dynamics diameter of CO2). After the pores are refined in step 2, the diameters of all pores are smaller than 0.330 nm.

[0077] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0078] The sodium ion battery negative electrode prepared in this embodiment has a first coulombic efficiency of up to 94%, a reversible specific capacity of up to 278 mAh / g, and a low potential platform specific capacity of 150 mAh / g.

[0079] Example 3

[0080] A method for preparing screening carbon comprises the following steps:

[0081] Step 1: First chemical vapor deposition to quickly reduce the pore size: porous carbon with rich pore structure (activated carbon fiber, small angle scattering test specific surface area is 1420m 2 / g, the specific surface area of ​​nitrogen adsorption and desorption test is 1380m 2 / g) was placed in a tube furnace, and argon gas with a flow rate of 90 ml / min was introduced, and the temperature was increased at a heating rate of 10°C / min to a final temperature of 1300°C; at the final temperature of 1300°C, methane gas with a flow rate of 30 ml / min was introduced, and the reaction was continued for 25 minutes to quickly seal the pore entrances on the porous carbon surface;

[0082] Step 2: Refine the pore opening to a diameter of less than 0.33 nm by a second chemical vapor deposition process: cut off the methane gas, cool to 700°C, introduce methane gas at a flow rate of 10 ml / min, and continue the reaction for 300 minutes. Further refine the pore entrance to a diameter of less than 0.33 nm.

[0083] Step 3, turning off the carbon source gas and cooling the temperature to room temperature at a cooling rate of 10°C / min to obtain the screening carbon.

[0084] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by small-angle X-ray scattering to be 1420 m 2 / g, the specific surface area of ​​the sieved carbon obtained in step 3 was measured by small angle X-ray scattering to be 1408m 2 / g, indicating that the deposited carbon from the two chemical vapor deposition phases did not enter the pore belly, achieving the effect of selectively adjusting the pore opening.

[0085] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by nitrogen adsorption and desorption to be 1380 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 21m 2 / g, after the second chemical vapor deposition, the specific surface area dropped to 5m 2 / g, indicating that after the rapid shrinkage of the pores in step 1, the diameters of most pores are smaller than 0.364 nm (the molecular dynamics diameter of N2). After the fine pores in step 2, the diameters of all pores are smaller than 0.364 nm.

[0086] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by carbon dioxide adsorption and desorption to be 1358 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 520m 2 / g, after the second chemical vapor deposition, the specific surface area dropped to 6m 2 / g, indicating that after the pores are rapidly reduced in step 1, the diameters of most pores are still larger than 0.330 nm (the molecular dynamics diameter of CO2). After the pores are refined in step 2, the diameters of all pores are smaller than 0.330 nm.

[0087] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0088] The sodium ion battery negative electrode prepared in this embodiment has a first coulombic efficiency of up to 92.5%, a reversible specific capacity of up to 348 mAh / g, and a low potential platform specific capacity of 272 mAh / g.

[0089] Example 4

[0090] A method for preparing screening carbon comprises the following steps:

[0091] Step 1: First chemical vapor deposition to quickly reduce the pore size: porous carbon with rich pore structure (coconut shell-based activated carbon, small angle scattering test specific surface area is 1800m 2 / g, the specific surface area of ​​nitrogen adsorption and desorption test is 1802m 2 / g) was placed in a tube furnace, and a protective gas of argon was introduced at a flow rate of 90 ml / min. The temperature was raised at a heating rate of 10°C / min to a final temperature of 1200°C. At the final temperature of 1200°C, methane gas was introduced at a flow rate of 30 ml / min, and the reaction was continued for 25 minutes to quickly seal the pore entrances on the porous carbon surface;

[0092] Step 2: Second chemical vapor deposition refinement of the pore to a diameter of less than 0.33 nm: cut off the methane gas, cool to 800 degrees, introduce methane gas at a flow rate of 10 ml / min, and continue the reaction for 300 minutes. The pore entrance is further refined to a diameter of less than 0.33 nm.

[0093] Step 3, turning off the carbon source gas and cooling the temperature to room temperature at a cooling rate of 10°C / min to obtain the screening carbon.

[0094] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by small-angle X-ray scattering to be 1800 m 2 / g, the specific surface area of ​​the sieved carbon obtained in step 3 was measured by small-angle X-ray scattering to be 1760m 2 / g, indicating that the deposited carbon from the two chemical vapor deposition phases did not enter the pore belly, achieving the effect of selectively adjusting the pore opening.

[0095] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by nitrogen adsorption and desorption to be 1802 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 45m 2 / g, and after the second chemical vapor deposition, the specific surface area dropped to 4.8m 2 / g, indicating that after the rapid shrinkage of the pores in step 1, the diameters of most pores are smaller than 0.364 nm (the molecular dynamics diameter of N2). After the fine pores in step 2, the diameters of all pores are smaller than 0.364 nm.

[0096] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by carbon dioxide adsorption and desorption to be 1770 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 820m 2 / g, after the second chemical vapor deposition, the specific surface area dropped to 7m 2 / g, indicating that after the pores are rapidly reduced in step 1, the diameters of most pores are still larger than 0.330 nm (the molecular dynamics diameter of CO2). After the pores are refined in step 2, the diameters of all pores are smaller than 0.330 nm.

[0097] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0098] The sodium ion battery negative electrode prepared in this embodiment has a first coulombic efficiency of up to 94%, a reversible specific capacity of up to 402 mAh / g, and a low potential platform specific capacity of 325 mAh / g.

[0099] Example 5

[0100] A method for preparing screening carbon comprises the following steps:

[0101] Step 1: First chemical vapor deposition to quickly reduce the pore size: porous carbon with rich pore structure (bamboo-based activated carbon, small angle scattering test specific surface area is 1650m 2 / g, the specific surface area of ​​nitrogen adsorption and desorption test is 1632m 2 / g) was placed in a tube furnace, and a protective gas of argon was introduced at a flow rate of 90 ml / min. The temperature was raised at a heating rate of 10°C / min to a final temperature of 1200°C. At the final temperature of 1200°C, methane gas was introduced at a flow rate of 30 ml / min, and the reaction was continued for 15 minutes to quickly seal the pore entrances on the porous carbon surface;

[0102] Step 2: Refine the orifice to a diameter of less than 0.33 nm by a second chemical vapor deposition process: cut off the methane gas, cool to 800°C, introduce methane gas at a flow rate of 10 ml / min, and continue the reaction for 300 minutes to further refine the orifice to a diameter of less than 0.33 nm.

[0103] Step 3, turning off the carbon source gas and cooling the temperature to room temperature at a cooling rate of 10°C / min to obtain the screening carbon.

[0104] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by small-angle X-ray scattering to be 1650 m 2 / g, the specific surface area of ​​the sieved carbon obtained in step 3 was measured by small angle X-ray scattering to be 1642m 2 / g, indicating that the deposited carbon from the two chemical vapor deposition phases did not enter the pore belly, achieving the effect of selectively adjusting the pore opening.

[0105] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by nitrogen adsorption and desorption to be 1632 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 68m 2 / g, after the second chemical vapor deposition, the specific surface area dropped to 5m 2 / g, indicating that after the rapid shrinkage of the pores in step 1, the diameters of most pores are smaller than 0.364 nm (the molecular dynamics diameter of N2). After the fine pores in step 2, the diameters of all pores are smaller than 0.364 nm.

[0106] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by carbon dioxide adsorption and desorption to be 1624 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 614m 2 / g, after the second chemical vapor deposition, the specific surface area dropped to 5m 2 / g, indicating that after the pores are rapidly reduced in step 1, the diameters of most pores are still larger than 0.330 nm (the molecular dynamics diameter of CO2). After the pores are refined in step 2, the diameters of all pores are smaller than 0.330 nm.

[0107] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0108] The sodium ion battery negative electrode prepared in this embodiment has a first coulombic efficiency of up to 93%, a reversible specific capacity of up to 367 mAh / g, and a low potential platform specific capacity of 290 mAh / g.

[0109] Example 6

[0110] A method for preparing screening carbon comprises the following steps:

[0111] Step 1: First chemical vapor deposition to quickly reduce the pore size: porous carbon with rich pore structure (petroleum coke-based activated carbon, small angle scattering test specific surface area is 2140m 2 / g, the specific surface area of ​​nitrogen adsorption and desorption test is 2125m 2 / g) was placed in a tube furnace, and a protective gas of argon was introduced at a flow rate of 90 ml / min. The temperature was raised at a heating rate of 10°C / min to a final temperature of 1200°C. At the final temperature of 1200°C, methane gas was introduced at a flow rate of 30 ml / min, and the reaction was continued for 25 minutes to quickly seal the pore entrances on the porous carbon surface;

[0112] Step 2: Refine the pore opening to a diameter of less than 0.33 nm by a second chemical vapor deposition process: cut off the methane gas, cool the temperature to 800°C, introduce methane gas at a flow rate of 10 ml / min, and continue the reaction for 240 minutes. Further refine the pore entrance to a diameter of less than 0.33 nm.

[0113] Step 3, turning off the carbon source gas and cooling the temperature to room temperature at a cooling rate of 10°C / min to obtain the screening carbon.

[0114] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by small-angle X-ray scattering to be 2140 m 2 / g, the specific surface area of ​​the sieve-type carbon obtained in step 3 was measured by small-angle X-ray scattering to be 2122m 2 / g, indicating that the deposited carbon from the two chemical vapor deposition phases did not enter the pore belly, achieving the effect of selectively adjusting the pore opening.

[0115] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by nitrogen adsorption and desorption to be 2125 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 75m 2 / g, after the second chemical vapor deposition, the specific surface area dropped to 5m 2 / g, indicating that after the rapid shrinkage of the pores in step 1, the diameters of most pores are smaller than 0.364 nm (the molecular dynamics diameter of N2). After the fine pores in step 2, the pore sizes of all pores are smaller than 0.364 nm.

[0116] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by carbon dioxide adsorption and desorption to be 2100 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 821m 2 / g, after the second chemical vapor deposition, the specific surface area dropped to 5m 2 / g, indicating that after the pores are rapidly reduced in step 1, the diameters of most pores are still larger than 0.330 nm (the molecular dynamics diameter of CO2). After the pores are refined in step 2, the diameters of all pores are smaller than 0.330 nm.

[0117] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0118] The sodium ion battery negative electrode prepared in this embodiment has a first coulombic efficiency of up to 94%, a reversible specific capacity of up to 425 mAh / g, and a low potential platform specific capacity of 350 mAh / g.

[0119] Example 7

[0120] A method for preparing screening carbon comprises the following steps:

[0121] Step 1: First chemical vapor deposition to quickly reduce the pore size: porous carbon with rich pore structure (coconut shell-based activated carbon, small angle scattering test specific surface area is 1800m 2 / g, the specific surface area of ​​nitrogen adsorption and desorption test is 1802m 2 / g) was placed in a tubular furnace, and a protective gas of argon was introduced at a flow rate of 90 ml / min, and the temperature was raised at a heating rate of 10°C / min to a final temperature of 1200°C; at the final temperature of 1200°C, natural gas was introduced at a flow rate of 30 ml / min, and the reaction was continued for 25 minutes to quickly seal the pore entrances on the porous carbon surface;

[0122] Step 2: Refine the pore opening to a diameter of less than 0.33 nm by a second chemical vapor deposition process: shut off the natural gas, cool the temperature to 800°C, introduce natural gas at a flow rate of 10 ml / min, and continue the reaction for 240 minutes. The pore entrance is further refined to a diameter of less than 0.33 nm.

[0123] Step 3, turning off the carbon source gas and cooling the temperature to room temperature at a cooling rate of 10°C / min to obtain the screening carbon.

[0124] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by small-angle X-ray scattering to be 1800 m 2 / g, the specific surface area of ​​the sieved carbon obtained in step 3 was measured by small-angle X-ray scattering to be 1795m 2 / g, indicating that the deposited carbon from the two chemical vapor deposition phases did not enter the pore belly, achieving the effect of selectively adjusting the pore opening.

[0125] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by nitrogen adsorption and desorption to be 1802 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 76m 2 / g, and after the second chemical vapor deposition, the specific surface area dropped to 3.5m 2 / g, indicating that after the rapid shrinkage of the pores in step 1, the diameters of most pores are smaller than 0.364 nm (the molecular dynamics diameter of N2). After the fine pores in step 2, the diameters of all pores are smaller than 0.364 nm.

[0126] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by carbon dioxide adsorption and desorption to be 1770 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 350m 2 / g, after the second chemical vapor deposition, the specific surface area dropped to 3m 2 / g, indicating that after the pores are rapidly reduced in step 1, the diameters of most pores are still larger than 0.330 nm (the molecular dynamics diameter of CO2). After the pores are refined in step 2, the diameters of all pores are smaller than 0.330 nm.

[0127] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0128] The sodium ion battery negative electrode prepared in this embodiment has a first coulombic efficiency of up to 95%, a reversible specific capacity of up to 410 mAh / g, and a low potential platform specific capacity of 330 mAh / g.

[0129] Example 8

[0130] A method for preparing screening carbon comprises the following steps:

[0131] Step 1: First chemical vapor deposition to quickly reduce the pore size: porous carbon with rich pore structure (coconut shell-based activated carbon, small angle scattering test specific surface area is 1800m 2 / g, the specific surface area of ​​nitrogen adsorption and desorption test is 1802m 2 / g) was placed in a tube furnace, and argon protective gas was introduced at a flow rate of 90 ml / min, and the temperature was increased at a heating rate of 10°C / min to a final temperature of 1200°C; at the final temperature of 1200°C, ethane was introduced at a flow rate of 30 ml / min, and the reaction was continued for 25 minutes to quickly seal the pore entrances on the porous carbon surface;

[0132] Step 2: Refine the pore opening to a diameter of less than 0.33 nm by a second chemical vapor deposition process: cut off the ethane, cool to 800°C, introduce ethane gas at a flow rate of 10 ml / min, and continue the reaction for 240 minutes. Further refine the pore entrance to a diameter of less than 0.33 nm.

[0133] Step 3, turning off the carbon source gas and cooling the temperature to room temperature at a cooling rate of 10°C / min to obtain the screening carbon.

[0134] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by small-angle X-ray scattering to be 1800 m 2 / g, the specific surface area of ​​the sieve-type carbon obtained in step 3 was measured by small-angle X-ray scattering to be 1772m 2 / g, indicating that the deposited carbon from the two chemical vapor deposition phases did not enter the pore belly, achieving the effect of selectively adjusting the pore opening.

[0135] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by nitrogen adsorption and desorption to be 1802 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 46m 2 / g, and after the second chemical vapor deposition, the specific surface area dropped to 3.9m 2 / g, indicating that after the rapid shrinkage of the pores in step 1, the diameters of most pores are smaller than 0.364 nm (the molecular dynamics diameter of N2). After the fine pores in step 2, the pore sizes of all pores are smaller than 0.364 nm.

[0136] In this embodiment, the specific surface area of ​​the porous carbon used in step 1 was measured by carbon dioxide adsorption and desorption to be 1770 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 632m 2 / g, after the second chemical vapor deposition, the specific surface area dropped to 4m 2 / g, indicating that after the pores are rapidly reduced in step 1, the diameters of most pores are still larger than 0.330 nm (the molecular dynamics diameter of CO2). After the pores are refined in step 2, the diameters of all pores are smaller than 0.330 nm.

[0137] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0138] The sodium ion battery negative electrode prepared in this embodiment has a first coulombic efficiency of up to 93.5%, a reversible specific capacity of up to 408 mAh / g, and a low potential platform specific capacity of 312 mAh / g.

[0139] Comparative Example 1

[0140] This comparative example is compared with Example 1, except that step 2 is not performed in Comparative Example 1.

[0141] The small angle X-ray scattering diagram of the carbon material obtained in Comparative Example 1 is shown in FIG8 . It can be seen that the specific surface area of ​​the porous carbon measured by small angle X-ray scattering is 1420 m 2 / g, the specific surface area of ​​the carbon material after the pore size was reduced by the above steps was measured by small-angle X-ray scattering to be 1418m 2 / g, indicating that after high-temperature rapid deposition, the pore structure of the material has not changed, and the deposited carbon at the entrance of the shrinkage pore has not entered the pore belly.

[0142] The nitrogen adsorption and desorption test diagram of the carbon material provided in Comparative Example 1 is shown in FIG9 . It can be seen that the specific surface area of ​​the porous carbon measured by nitrogen adsorption and desorption is 1380 m 2 / g, the specific surface area of ​​the carbon material after the pore size is reduced by the above steps is reduced to 30m 2 / g, most of the pore diameters are smaller than 0.364nm (molecular dynamics diameter of N2).

[0143] The carbon dioxide adsorption and desorption test diagram of the carbon material provided in Comparative Example 1 is shown in FIG10 . It can be seen that the specific surface area of ​​the porous carbon by carbon dioxide adsorption and desorption is 1358 m 2 / g, and the specific surface area of ​​the carbon material after the pore size is reduced by the above steps is reduced to 600m 2 / g, indicating that after the pore size is rapidly reduced in step 1, the diameters of most pores are still larger than 0.330 nm (the molecular dynamics diameter of CO2).

[0144] The TEM image of the carbon material provided in Comparative Example 1 is shown in FIG11 . It can be seen that before and after the pore size is reduced, the internal structure of the pore does not change, and the deposited carbon does not enter the pore belly, thus achieving a selective effect.

[0145] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0146] The first cycle charge and discharge curve of the sodium ion battery negative electrode prepared in this comparative example is shown in FIG12 . It can be seen that the prepared sodium ion battery type carbon negative electrode material has an initial coulombic efficiency of only 78%, a reversible specific capacity of 258 mAh / g, and a low potential platform specific capacity of 101 mAh / g.

[0147] Comparative Example 2

[0148] This comparative example is compared with Example 1, except that, in comparative example 2, the reaction time during step 1 is 1 h, and step 2 is not performed.

[0149] As shown in Figure 13, the specific surface area of ​​the porous carbon was measured by small-angle X-ray scattering to be 1420 m 2 / g, and the specific surface area of ​​the carbon material after being treated by the steps of Comparative Example 2 was measured by small-angle X-ray scattering to be 689m 2 / g, indicating that after high-temperature rapid deposition, the pore structure of the material changes, and the deposited carbon used to shrink the pore mouth partially enters the pores, filling the pores and reducing the pore volume.

[0150] The specific surface area of ​​porous carbon was measured by nitrogen adsorption and desorption to be 1380 m 2 / g, the specific surface area of ​​the carbon material after the pore size is partially shrunk by the above steps is reduced to 18m 2 / g, indicating that most of the pore diameters are smaller than 0.364nm (the molecular dynamics diameter of N2).

[0151] As shown in Figure 14, the specific surface area of ​​the porous carbon measured by carbon dioxide adsorption and desorption is 1358m 2 / g, and the specific surface area of ​​the carbon material after the pore size is partially shrunk by the above steps is reduced to 500m 2 / g, indicating that some pore sizes are still larger than 0.330nm (molecular dynamics diameter of CO2). At the same time, due to the filling of deposited carbon inside the pore structure, the pore volume decreases and the internal specific surface area decreases significantly.

[0152] The TEM images of porous carbon before and after preparation are shown in Figure 15. It can be seen that before and after the pore mouth is shrunk, the internal structure of the pore changes significantly, the deposited carbon partially enters the pore belly, and the deposition selectivity is poor.

[0153] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0154] The first cycle charge and discharge curve of the sodium ion battery negative electrode prepared in this comparative example is shown in FIG16 . It can be seen that the carbon material obtained in this comparative example has an initial coulombic efficiency of only 45%, a reversible specific capacity of 210 mAh / g, and a low potential platform specific capacity of 54 mAh / g.

[0155] Comparative Example 3

[0156] This comparative example is compared with Example 1, except that, in comparative example 3, the reaction time during step 1 is 2 h, and step 2 is not performed.

[0157] The specific surface area of ​​the porous carbon was measured by small-angle X-ray scattering to be 1420 m 2 / g, and the specific surface area of ​​the carbon material after the pore size was partially shrunk by the above steps was measured by small-angle X-ray scattering to be 294m 2 / g, indicating that after high-temperature rapid deposition, the pore structure of the material changes, and the deposited carbon used to shrink the pore mouth partially enters the pores, filling the pores and reducing the pore volume.

[0158] The specific surface area of ​​porous carbon was measured by nitrogen adsorption and desorption to be 1380 m 2 / g, the specific surface area of ​​the carbon material after the pore size is partially shrunk by the above steps is reduced to 7m 2 / g, indicating that most of the pore diameters are smaller than 0.364nm (the molecular dynamics diameter of N2).

[0159] The specific surface area of ​​porous carbon measured by carbon dioxide adsorption and desorption is 1358m 2 / g, the specific surface area of ​​the carbon material after the pore size is partially shrunk by the above steps is reduced to 16m 2 / g, indicating that only a few pore sizes are larger than 0.330 nm (the molecular dynamics diameter of CO2).

[0160] Similar to Comparative Example 2, the internal structure changes significantly before and after the pore mouth shrinks, and a large amount of deposited carbon enters the pore belly, causing a large amount of pore structure to disappear.

[0161] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0162] The sodium ion battery negative electrode prepared in this comparative example has an initial coulombic efficiency of only 45% and a reversible specific capacity of 170 mAh / g, of which the low potential platform specific capacity is 34 mAh / g.

[0163] Comparative Example 4

[0164] This comparative example is compared with Example 1, except that, in comparative example 4, the temperature of the first chemical vapor deposition in step 1 is 900°C, and the reaction is continued for 25 minutes. Step 2 is the same as Example 1, and the temperature of the second chemical vapor deposition is 700°C, and the reaction is continued for 300 minutes.

[0165] The specific surface area of ​​the porous carbon was measured by small-angle X-ray scattering to be 1420 m 2 / g, and the specific surface area of ​​the carbon material after the pore size was partially shrunk by the above steps was measured by small-angle X-ray scattering to be 1410m 2 / g, indicating that the deposited carbon used to shrink the pore mouth did not enter the pore belly, achieving the effect of selectively adjusting the pore mouth.

[0166] The specific surface area of ​​porous carbon was measured by nitrogen adsorption and desorption to be 1380 m 2 / g, after the first chemical vapor deposition in step 1, the specific surface area of ​​the carbon material is reduced to 500m 2 / g, after the second chemical vapor deposition in step 2, the specific surface area is reduced to 21m2 / g, indicating that after the treatment in step 1, the pore diameters of most pores are still larger than 0.364 nm (the molecular dynamics diameter of N2), and after the treatment in step 2, the pore diameters of some pores are still larger than 0.364 nm.

[0167] The specific surface area of ​​porous carbon measured by carbon dioxide adsorption and desorption is 1358m 2 / g, after the first chemical vapor deposition in step 1, the specific surface area of ​​the carbon material is reduced to 900m 2 / g, after the second chemical vapor deposition in step 2, the specific surface area is reduced to 40m 2 / g, indicating that after the treatment in step 1, the pore diameters of most pores are still larger than 0.330 nm (molecular dynamics diameter of CO2). After the treatment in step 2, the pore diameters of some pores are still larger than 0.330 nm.

[0168] Similar to Comparative Example 1, the internal structure did not change before and after the pore mouth was shrunk, and the deposited carbon did not enter the pore belly, achieving a selective effect.

[0169] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0170] The sodium ion battery negative electrode prepared in this comparative example has an initial coulombic efficiency of only 82% and a reversible specific capacity of 304 mAh / g, of which the low potential platform specific capacity is 230 mAh / g.

[0171] Comparative Example 5

[0172] This comparative example is compared with Example 1, except that, in comparative example 5, the temperature of the first chemical vapor deposition in step 1 is 1000°C, and the reaction is continued for 25 minutes. Step 2 is the same as Example 1, and the temperature of the second chemical vapor deposition is 700°C, and the reaction is continued for 300 minutes.

[0173] The specific surface area of ​​the porous carbon was measured by small-angle X-ray scattering to be 1420 m 2 / g, and the specific surface area of ​​the carbon material obtained after the above steps was measured by small-angle X-ray scattering to be 1412m 2 / g, indicating that the deposited carbon in the two-step chemical vapor deposition did not enter the pore belly, achieving the effect of selectively adjusting the pore opening.

[0174] The specific surface area of ​​porous carbon was measured by nitrogen adsorption and desorption to be 1380 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 395m 2 / g, and after the second chemical vapor deposition, the specific surface area dropped to 16m 2 / g, after the first chemical vapor deposition, the pore size of some pores is still larger than 0.364nm (molecular dynamics diameter of N2), and after the second chemical vapor deposition, the pore size of a small number of pores is still larger than 0.364nm.

[0175] The specific surface area of ​​porous carbon measured by carbon dioxide adsorption and desorption is 1358m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 647m 2 / g, and after the second chemical vapor deposition, the specific surface area dropped to 29m 2 / g, indicating that after the treatment in step 1, the pore diameters of most of the obtained carbon materials are still larger than 0.330 nm (the molecular dynamics diameter of CO2). After the treatment in step 2, there are still a few pores with pore sizes larger than 0.330 nm.

[0176] After two chemical vapor depositions, similar to comparative example 1, the internal structure did not change, and the deposited carbon did not enter the pores, achieving a selective effect.

[0177] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0178] The sodium ion battery negative electrode prepared in this comparative example has an initial coulombic efficiency of 87%, a reversible specific capacity of 332 mAh / g, and a low potential platform specific capacity of 253 mAh / g.

[0179] Comparative Example 6

[0180] This comparative example is compared with Example 1. Step 1 is the same as Example 1, except that the temperature of the second chemical vapor deposition in step 2 is 700° C., and the reaction is continued for 2 hours.

[0181] The specific surface area of ​​the porous carbon was measured by small-angle X-ray scattering to be 1420 m 2 / g, and the specific surface area of ​​the carbon material treated by the steps of Comparative Example 6 was measured by small-angle X-ray scattering to be 1420m 2 / g, indicating that the deposited carbon used to shrink the pore mouth did not enter the pore belly, achieving the effect of selectively adjusting the pore mouth.

[0182] The specific surface area of ​​porous carbon was measured by nitrogen adsorption and desorption to be 1380 m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 35m 2 / g, and after the second chemical vapor deposition, the specific surface area dropped to 16m 2 / g, indicating that after the treatment in step 1, the pore size of most pores is smaller than 0.364 nm (the molecular dynamics diameter of N2), and after the treatment in step 2, the pore size of a small number of pores is still larger than 0.364 nm.

[0183] The specific surface area of ​​porous carbon measured by carbon dioxide adsorption and desorption is 1358m 2 / g, after the first chemical vapor deposition, the specific surface area dropped to 632m 2 / g, and after the second chemical vapor deposition, the specific surface area dropped to 241m 2 / g, indicating that after the treatment in step 1, most of the pore diameters are still larger than 0.330nm (the molecular dynamics diameter of CO2). After the treatment in step 2, there are still a considerable number of pores with pore sizes larger than 0.330nm.

[0184] Before and after the two chemical vapor depositions, similar to Comparative Example 1, the internal structure did not change, and the deposited carbon did not enter the pores, achieving a selective effect.

[0185] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0186] The sodium ion battery negative electrode prepared in this comparative example has an initial coulombic efficiency of 79%, a reversible specific capacity of 301 mAh / g, and a low potential platform specific capacity of 212 mAh / g.

[0187] Comparative Example 7

[0188] This comparative example is compared with Example 1. Step 1 is the same as Example 1, except that the temperature of the second chemical vapor deposition in step 2 is 900° C., and the reaction is continued for 5 hours.

[0189] The specific surface area of ​​the porous carbon was measured by small-angle X-ray scattering to be 1420 m 2 / g, and the specific surface area of ​​the carbon material after the pore size was partially shrunk by the above steps was measured by small-angle X-ray scattering to be 1023m 2 / g, indicating that part of the deposited carbon used to shrink the pore mouth entered the interior of the pore and failed to achieve the effect of selectively adjusting the pore mouth.

[0190] The specific surface area of ​​porous carbon was measured by nitrogen adsorption and desorption to be 1380 m 2 / g, after the first chemical vapor deposition in step 1, the specific surface area is reduced to 37m 2 / g, after the second chemical vapor deposition in step 2, the specific surface area is reduced to 3m 2 / g, after the treatment in step 1, the pore size of most pores is smaller than 0.364nm (molecular dynamics diameter of N2), and after the treatment in step 2, the pore size of all pores is smaller than 0.364nm.

[0191] The specific surface area of ​​porous carbon measured by carbon dioxide adsorption and desorption is 1358m 2 / g, after the first chemical vapor deposition in step 1, the specific surface area is reduced to 612m 2 / g, after the second chemical vapor deposition in step 2, the specific surface area is reduced to 4m 2 / g, after the treatment in step 1, the pore diameters of most pores are still larger than 0.330nm (molecular dynamics diameter of CO2), and after the treatment in step 2, the pore diameters of all pores are smaller than 0.330nm.

[0192] Similar to Comparative Example 2, the internal structure changes before and after the pore mouth shrinks, and the deposited carbon enters the pore belly, failing to achieve a selectivity effect.

[0193] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0194] The sodium ion battery negative electrode prepared in this comparative example has an initial coulombic efficiency of 73%. Although the pore diameters are all less than 0.330 nm, the initial coulombic efficiency is reduced due to excessive carbon deposition. The reversible specific capacity is 278 mAh / g, of which the low-potential platform specific capacity is 139 mAh / g.

[0195] Comparative Example 8

[0196] This comparative example is compared with Example 1. Step 1 is the same as Example 1, except that the temperature of the second chemical vapor deposition in step 2 is 500° C., and the reaction is continued for 5 hours.

[0197] The specific surface area of ​​the porous carbon was measured by small-angle X-ray scattering to be 1420 m 2 / g, and the specific surface area of ​​the carbon material after the pore size was partially shrunk by the above steps was measured by small-angle X-ray scattering to be 1407m 2 / g, indicating that the deposited carbon used to shrink the pore mouth did not enter the pore belly.

[0198] The specific surface area of ​​porous carbon was measured by nitrogen adsorption and desorption to be 1380 m 2 / g, after the first chemical vapor deposition in step 1, the specific surface area is reduced to 37m 2 / g, after the second chemical vapor deposition in step 2, the specific surface area is reduced to 29m 2 / g, indicating that after the treatment in step 1, the size of most pores is smaller than 0.364 nm (molecular dynamics diameter of N2).

[0199] The specific surface area of ​​porous carbon measured by carbon dioxide adsorption and desorption is 1358m 2 / g, after the first chemical vapor deposition in step 1, the specific surface area is reduced to 596m 2 / g, after the second chemical vapor deposition in step 2, the specific surface area is reduced to 274m 2 / g, indicating that after the treatment in step 1, most of the pore diameters are still larger than 0.330nm (molecular dynamics diameter of CO2). After the treatment in step 2, some pores still have pore sizes larger than 0.330nm. The pore plugging effect of the low-temperature deposition process is poor and the pore size cannot be effectively reduced.

[0200] The same method as in Example 1 was used to assemble a 2032 button-type battery, and its electrochemical performance was tested.

[0201] The sodium ion battery negative electrode prepared in this comparative example has an initial coulombic efficiency of 82%, a reversible specific capacity of 285 mAh / g, and a low potential platform specific capacity of 124 mAh / g.

[0202] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing the screening carbon, characterized in that: The following steps are involved: Step 1: Rapidly shrink the pores by first chemical vapor deposition: Place the porous carbon in a chemical vapor deposition apparatus, introduce a predetermined flow of protective gas, raise the temperature to 1100-1300°C, then introduce a predetermined flow of a first carbon source gas at a flow rate of 10-500 ml / min, and perform a first heat preservation, wherein the first heat preservation time is 0-30 minutes and is not 0; Step 2, a second chemical vapor deposition process to refine the orifice to a diameter of less than 0.33 nm: After the first heat preservation is completed, the first carbon source gas is cut off, the temperature is lowered to 600-800°C, and a predetermined flow rate of the second carbon source gas is introduced, the flow rate of the second carbon source gas being ≥10 ml / min, and a second heat preservation is performed, the second heat preservation time being ≥3 hours; Step 3: Turn off the second carbon source gas and cool the temperature to room temperature at a predetermined cooling rate to obtain the screening carbon.

2. The method for preparing screening carbon according to claim 1, wherein: The porous carbon in step 1 is walnut shell-based porous carbon, bamboo-based activated carbon, coconut shell-based porous carbon, peanut shell-based porous carbon, petroleum coke-based porous carbon, needle coke-based porous carbon or activated carbon fiber.

3. The method for preparing screening carbon according to claim 1, wherein: In step 1, the first carbon source gas is methane, benzene vapor, toluene vapor, xylene vapor, ethane, propane or acetylene; The second carbon source gas in step 2 is methane, benzene vapor, toluene vapor, xylene vapor, ethane, propane or acetylene.

4. The method for preparing screening carbon according to claim 1, characterized in that: After completing step 1, the specific surface area of the N2 adsorption and desorption test is 0-100m 2 / g, the specific surface area of CO2 adsorption and desorption test is 100-2000m 2 / g, and the pore diameter is 0.33-0.364nm.

5. The method for preparing screening carbon according to claim 1, wherein: After the orifice is refined in step 2, the orifice size of all holes is closed to the point where CO2 cannot enter. The specific surface area of the CO2 adsorption and desorption test is 0-10m 2 / g, and the pore diameters are all less than 0.33nm.

6. The method for preparing screening carbon according to claim 1, wherein: The pore size of the sieve-type carbon obtained in step 3 is consistent with the pore size of the porous carbon in step 1.

7. The screening carbon obtained by the preparation method according to any one of claims 1 to 6, characterized in that: The pores and periphery of the pores of the screening carbon are deposited with primary deposited carbon, and the surface of the primary deposited carbon is deposited at the position of the pores. The secondary deposited carbon does not enter the pores. After the two depositions, the diameter of the pores is less than 0.33 nm. The specific surface area of the screening carbon after CO2 adsorption and desorption test is 0-10 m 2 / g.

8. The screening carbon according to claim 7, characterized in that The pore diameter of the screening carbon is 0.5-10 nm.

9. Use of the sieve-type carbon as claimed in claim 7 in a negative electrode of a battery.

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