A doped modified hard carbon material and its preparation method and application

Abstract

This article discloses a doped and modified hard carbon material, its preparation method and application, which belongs to the field of new energy material technology. The preparation method described in this article uses a discharge plasma assisted ball milling process to sequentially dope oxygen atoms and sulfur atoms in the pre-carbonized raw material, and then after calcining to form a hard carbon material, a discharge plasma assisted oscillating vibration process is used to further carbon-coat the doped material. Not only does it not require special chemical reagents to produce waste liquid, but it also has low production energy consumption. Due to the doping of oxygen and sulfur atoms and the carbon layer coating modification, the product has a large interlayer spacing and many pore sites for sodium ion storage. At the same time, the specific surface area is moderate, and when used in sodium ion batteries, it exhibits high sodium storage capacity and first coulomb efficiency.

Description

Technical Field

[0001] This article relates to the field of new energy material technology, and in particular to a doped and modified hard carbon material and its preparation method and application. Background Art

[0002] Compared with lithium-ion batteries, sodium-ion batteries have the advantages of low production costs and a wide range of raw material sources. However, due to the poor storage efficiency of sodium ions in existing traditional graphite negative electrodes, if they are to replace the currently widely used lithium-ion batteries, further research and development of negative electrode materials that are conducive to sodium ion storage is still needed.

[0003] Hard carbon material is a material that is difficult to graphitize above 2500°C. This material has a large interlayer spacing and a porous structure, so in theory it is very suitable as a negative electrode material for sodium ion batteries. However, the first coulombic efficiency of hard carbon materials is low, and the actual effect of use is not ideal, so it needs to be further modified. Common methods for modifying hard carbon materials include doping with heterogeneous atoms (such as O / S / P atoms) and coating with carbon layers prepared with additional carbon sources. These methods can improve the first coulombic efficiency of the product, but they often involve high-temperature decomposition methods or the addition of additional chemical reagents. The overall process has high energy consumption and high production costs. In addition, if the waste liquid produced is not treated in time, it will be detrimental to the environment, and it is impossible to efficiently realize the integrated process of material production-processing-application. Summary of the Invention

[0004] The purpose of this article is to overcome the shortcomings of the above-mentioned existing technologies and provide a preparation method for doped modified hard carbon materials. This method uses a discharge plasma assisted ball milling process to sequentially dope oxygen atoms and sulfur atoms in the pre-carbonized raw materials. Subsequently, after calcination to form a hard carbon material, a discharge plasma assisted oscillating vibration process is used to further carbon-coat the doped material. Not only does it not require special chemical reagents to produce waste liquid, but it also has low production energy consumption, high first coulomb efficiency of the product, rich sodium ion storage sites, and high reversible capacity.

[0005] To achieve the above objectives, the technical solutions adopted in this paper are:

[0006] A method for preparing a doped and modified hard carbon material comprises the following steps:

[0007] The pre-carbonized carbon source is placed in a ball milling device containing an oxygen atmosphere and subjected to mechanical ball milling treatment under discharge conditions to obtain an oxygen-doped carbon material;

[0008] The oxygen-doped carbon material is placed in a ball milling device containing a hydrogen sulfide atmosphere and subjected to mechanical ball milling treatment under discharge conditions to obtain a sulfur-doped and oxygen-doped carbon material;

[0009] The sulfur-doped and oxygen-doped carbon material is kept at 1500-1700° C. for 15-25 hours under a protective atmosphere to obtain a doped hard carbon material;

[0010] The doped hard carbon material is placed in a vibration device containing acetylene atmosphere and subjected to oscillatory vibration treatment under discharge conditions to obtain the doped modified hard carbon material.

[0011] In the preparation method of the doped modified hard carbon material described in the present invention, the pre-carbonized carbon source is first subjected to discharge ball milling treatment in a device containing an oxygen atmosphere. Under the discharge conditions, oxygen will be converted into plasma and react with the surface of the carbon source to form oxygen-containing functional groups. This functional group can inhibit the graphitization of the carbon source in the subsequent hard carbonization process, so that the interlayer spacing is expanded, and it can also provide sodium storage active sites (carbon oxygen groups will react with sodium ions to form -CO-Na bonds); on the other hand, the carbon source not only becomes smaller in size during this process, but also due to the etching of the plasma, a large number of pore structures will be generated on the surface, providing sufficient active sites for sodium ion storage. Subsequently, in a similar treatment process, hydrogen sulfide is converted into sulfur plasma, which reacts with the carbon of the carbon source and forms carbon-sulfur bonds, and some of the excess carbon-oxygen bonds formed in the previous step will also react with the plasma and be converted into carbon-sulfur bonds and water vapor, and the doping of sulfur elements will further expand the interlayer spacing of the material. The element doping process does not need to be carried out in a high temperature environment, nor does it need to introduce a doping source in the form of a chemical agent.

[0012] At the same time, the process order of oxygen doping and sulfur doping cannot be swapped or carried out simultaneously, otherwise the obtained sulfur-doped and oxygen-doped carbon material will contain too many carbon-oxygen bonds, resulting in an increase in the irreversible capacity of the product and a decrease in the first coulombic efficiency.

[0013] After doping the two elements and completing the hard carbon conversion, acetylene gas is converted into carbon plasma under discharge conditions using acetylene gas as raw material, and then decomposed into carbon (C2H2→C+H2). Under the oscillating vibration process, a carbon coating layer is uniformly deposited on the surface of the doped hard carbon precursor. Under the said coating modification, the specific surface area of ​​the final product is reduced. After being applied to sodium ion batteries, the amount of SEI film formed on its surface during the first charge and discharge process is reduced, and the overall first coulombic efficiency is improved.

[0014] In one embodiment, the carbon source is at least one of phenolic resin, epoxy resin, glucose, and sucrose.

[0015] The type of carbon source selected in this article can be selected according to actual conditions and does not need to be specifically limited. Other types used in the preparation of existing common hard carbon materials can also be selected.

[0016] In one embodiment, the carbon source is pre-carbonized at a temperature of 400-600° C. for a time of 4-8 hours.

[0017] In one embodiment, the ball milling device is a high-energy ball mill. When preparing oxygen-doped carbon materials, the ball milling speed of the high-energy ball mill is 1000-1200 r / min, the ball milling time is 1-3 hours, and the ball-to-material ratio is (8-12):1.

[0018] Furthermore, the ball milling time is 1 to 3 hours.

[0019] Furthermore, the ball milling time is 1.5 to 2.5 hours.

[0020] Furthermore, when preparing the oxygen-doped carbon material, the discharge frequency of the high-energy ball mill is 15-25 kHz, the discharge voltage is 14-16 kV, and the discharge current is 1-3 A.

[0021] Furthermore, the discharge current is 1.5-2.5A.

[0022] Furthermore, when preparing the oxygen-doped carbon material, the pressure of the oxygen atmosphere in the high-energy ball mill is 0.6-1 MPa.

[0023] Furthermore, the pressure of the oxygen atmosphere is 0.7-0.9 MPa.

[0024] Under appropriate atmosphere pressure, discharge conditions and ball milling conditions, oxygen plasma can effectively etch and dope the surface of the carbon source.

[0025] In one embodiment, the ball milling device is a high-energy ball mill. When preparing sulfur-doped and oxygen-doped carbon materials, the ball milling speed of the high-energy ball mill is 1000-1200 r / min, the ball milling time is 1-3 hours, and the ball-to-material ratio is (8-12):1.

[0026] Furthermore, the ball milling time is 1.5 to 2.5 hours.

[0027] Furthermore, when preparing sulfur-doped and oxygen-doped carbon materials, the discharge frequency of the high-energy ball mill is 15-25 kHz, the discharge voltage is 14-16 kV, and the discharge current is 1-3 A.

[0028] Furthermore, the discharge current is 1.5-2.5A.

[0029] Furthermore, when preparing the sulfur-doped and oxygen-doped carbon material, the pressure of the hydrogen sulfide atmosphere in the high-energy ball mill is 0.6-1 MPa.

[0030] Furthermore, the pressure of the hydrogen sulfide atmosphere is 0.7-0.9 MPa.

[0031] Similar to the oxygen doping stage, during the sulfur doping process, as the ball milling time increases, the discharge conditions improve or the atmosphere pressure increases, the surface pores and interlayer spacing of the final product will increase, but the relative specific surface area will also increase, which is not conducive to ensuring the improvement of the first coulombic efficiency; on the other hand, excessive sulfur doping will lead to an increase in the defect concentration in the material and an increase in the irreversible capacity, so it is necessary to select a suitable processing technology.

[0032] In one embodiment, the oxygen content of the sulfur-doped and oxygen-doped carbon material is 11-17 wt %, and the sulfur content is 1-5 wt %.

[0033] In one embodiment, the specific surface area of ​​the sulfur-doped and oxygen-doped carbon material is 350 to 700 m 2 / g.

[0034] In one embodiment, the vibration device is a high-energy ball mill without ball milling beads. When preparing the doped and modified hard carbon material, the oscillation vibration rate of the high-energy ball mill is 1000-1200 r / min, and the oscillation vibration time is 1-3 h.

[0035] Furthermore, the oscillation vibration time is 1.5 to 2.5 hours.

[0036] Furthermore, when preparing the doped modified hard carbon material, the discharge frequency of the high-energy ball mill is 15-25 kHz, the discharge voltage is 14-16 kV, and the discharge current is 1-3 A.

[0037] Furthermore, the discharge current is 1.5-2.5A.

[0038] Furthermore, when preparing the doped modified hard carbon material, the pressure of the acetylene atmosphere in the high-energy ball mill is 0.3-0.7 MPa.

[0039] Furthermore, the pressure of the acetylene atmosphere is 0.4-0.6 MPa.

[0040] As the deposition process of the outermost carbon coating, since the carbon source is plasmatized acetylene, suitable vibration deposition conditions are also required to achieve uniform deposition. If the vibration time is too long, or the discharge conditions are improved and the atmosphere pressure is increased, the degree of acetylene deposition will increase. Although it will effectively reduce the final specific surface area of ​​the product and make the volume of the SEI film generated on its surface smaller, an excessively thick carbon layer will affect the transmission of sodium ions and reduce the active sodium storage sites of the overall product, resulting in a decrease in the material capacity.

[0041] Another object of this invention is to provide a doped and modified hard carbon material prepared by the method for preparing the doped and modified hard carbon material.

[0042] In one embodiment, the specific surface area of ​​the doped modified hard carbon material is 0.6 to 9.5 m2 / g, true density is 1.4~1.85g / cm 3 , the closed cell area is 0.08~0.28cm 3 / g.

[0043] In one embodiment, the interlayer spacing of the doped and modified hard carbon material is 3.9-4.3 nm.

[0044] The doped hard carbon material described in this article has moderate oxygen and sulfur doping content, large interlayer spacing in the crystal planes, and multiple pore structures, which can fully provide sufficient active sites for the storage of sodium ions; at the same time, under the modification of carbon coating, the specific surface area of ​​the product is moderate, which can effectively suppress the low first coulombic efficiency during the charging and discharging process.

[0045] Another object of this document is to provide a sodium ion battery, comprising a negative electrode plate, wherein the negative electrode plate comprises the doped modified hard carbon material described herein.

[0046] Compared with the existing technology, the beneficial effects of this article are:

[0047] This article provides a preparation method for doped and modified hard carbon materials. This method uses a discharge plasma-assisted ball milling process to sequentially dope oxygen atoms and sulfur atoms in the pre-carbonized raw material. Subsequently, after calcination to form a hard carbon material, the doped material is further carbon-coated using a discharge plasma-assisted oscillatory vibration process. This method not only does not require special chemical reagents to produce waste liquid, but also has low production energy consumption. Due to the doping of oxygen and sulfur atoms and the carbon layer coating modification, the product has a large interlayer spacing and many pore sites for sodium ion storage inside. At the same time, the specific surface area is moderate. When used in sodium ion batteries, the first coulomb efficiency is high and the reversible capacity is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is an infrared spectrum of the carbon source and the oxygen-doped carbon material in the preparation method of Example 1 described herein.

[0049] Figure 2 The XRD spectra of the products prepared in Example 1 and Comparative Example 1 described herein are shown. DETAILED DESCRIPTION

[0050] To better illustrate the purpose, technical solutions and advantages of this article, this article will be further described below with reference to the accompanying drawings and specific embodiments.

[0051] Unless otherwise specified, the materials used in the examples and comparative examples can be obtained through commercial channels.

[0052] The phenolic resin is 2123 thermosetting phenolic resin, and the epoxy resin is E44 (6101) epoxy resin.

[0053] Example 1

[0054] An embodiment of the doped and modified hard carbon material and its preparation method and application described herein is as follows:

[0055] (1) The carbon source obtained by pre-carbonizing phenolic resin at 500°C for 6 hours under a nitrogen atmosphere was placed in a high-energy ball mill containing an oxygen atmosphere at a pressure of 0.8 MPa, and mechanically ball milled for 2 hours under the discharge conditions of a ball mill discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A to obtain an oxygen-doped carbon material; the rotation speed during the mechanical ball milling was 1100 r / min, and the ball-to-material ratio of the ball milling beads was 10:1;

[0056] (2) placing the oxygen-doped carbon material in a high-energy ball mill containing a hydrogen sulfide atmosphere at a pressure of 0.8 MPa, and subjecting the material to mechanical ball milling for 2 h under the discharge conditions of a ball mill discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A, to obtain a sulfur-doped and oxygen-doped carbon material; the rotation speed during the mechanical ball milling treatment was 1100 r / min, and the ball-to-material ratio of the ball milling beads was 10:1;

[0057] (3) heating the sulfur-doped and oxygen-doped carbon material to 1600°C in a nitrogen atmosphere and maintaining the temperature for 20 hours to obtain a doped hard carbon material;

[0058] (4) The doped hard carbon material is placed in a high-energy ball mill containing an acetylene atmosphere at a pressure of 0.5 MPa without placing ball mill beads, and subjected to oscillatory vibration treatment under the discharge conditions of the ball mill at a discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A to obtain a doped modified hard carbon material; the rotation speed of the ball mill during the oscillatory vibration treatment is 1100 r / min.

[0059] Example 2

[0060] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the mechanical ball milling treatment time in step (1) is 1 hour.

[0061] Example 3

[0062] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from Example 1 only in that the mechanical ball milling treatment time in step (1) is 3 hours.

[0063] Example 4

[0064] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the discharge current in step (1) is 1A.

[0065] Example 5

[0066] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the discharge current in step (1) is 3A.

[0067] Example 6

[0068] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the pressure of the oxygen atmosphere in step (1) is 0.6 MPa.

[0069] Example 7

[0070] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the pressure of the oxygen atmosphere in step (1) is 1 MPa.

[0071] Example 8

[0072] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the mechanical ball milling treatment time in step (2) is 1 hour.

[0073] Example 9

[0074] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the mechanical ball milling treatment time in step (2) is 3 hours.

[0075] Example 10

[0076] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the discharge current in step (2) is 1A.

[0077] Example 11

[0078] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the discharge current in step (2) is 3A.

[0079] Example 12

[0080] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the pressure of the hydrogen sulfide atmosphere in step (2) is 0.6 MPa.

[0081] Example 13

[0082] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the pressure of the hydrogen sulfide atmosphere in step (2) is 1 MPa.

[0083] Example 14

[0084] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the oscillating vibration treatment time in step (4) is 1 hour.

[0085] Example 15

[0086] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the oscillating vibration treatment time in step (4) is 3 hours.

[0087] Example 16

[0088] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the discharge current in step (4) is 1A.

[0089] Example 17

[0090] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from embodiment 1 only in that the discharge current in step (4) is 3A.

[0091] Example 18

[0092] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from Example 1 only in that the pressure of the acetylene atmosphere in step (4) is 0.3 MPa.

[0093] Example 19

[0094] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from Example 1 only in that the pressure of the acetylene atmosphere in step (4) is 0.7 MPa.

[0095] Example 20

[0096] An embodiment of the doped and modified hard carbon material, preparation method, and application thereof described herein differs from Example 1 only in that the phenolic resin used in the carbon source preparation is replaced by epoxy resin.

[0097] Comparative Example 1

[0098] A hard carbon material and its preparation method and application, wherein the preparation method of the hard carbon material is as follows:

[0099] (1) The carbon source obtained by pre-carbonizing phenolic resin at 500°C for 6 hours under a nitrogen atmosphere was placed in a high-energy ball mill containing an argon atmosphere at a pressure of 0.8 MPa and mechanically ball-milled for 4 hours to obtain a ball-milled carbon material;

[0100] (3) The ball-milled carbon material was heated to 1600°C in a nitrogen atmosphere and kept at this temperature for 20 hours to obtain a hard carbon material.

[0101] Comparative Example 2

[0102] A doped hard carbon material and its preparation method and application, the preparation method of the doped hard carbon material is as follows:

[0103] (1) The carbon source obtained by pre-carbonizing phenolic resin at 500°C for 6 hours under a nitrogen atmosphere was placed in a high-energy ball mill containing an oxygen atmosphere at a pressure of 0.8 MPa, and mechanically ball milled for 2 hours under the discharge conditions of a ball mill discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A to obtain an oxygen-doped carbon material; the rotation speed during the mechanical ball milling was 1100 r / min, and the ball-to-material ratio of the ball milling beads was 10:1;

[0104] (2) placing the oxygen-doped carbon material in a high-energy ball mill containing a hydrogen sulfide atmosphere at a pressure of 0.8 MPa, and subjecting the material to mechanical ball milling for 2 h under the discharge conditions of a ball mill discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A, to obtain a sulfur-doped and oxygen-doped carbon material; the rotation speed during the mechanical ball milling treatment was 1100 r / min, and the ball-to-material ratio of the ball milling beads was 10:1;

[0105] (3) The sulfur-doped and oxygen-doped carbon material is heated to 1600°C in a nitrogen atmosphere and kept at this temperature for 20 hours to obtain a doped hard carbon material.

[0106] Comparative Example 3

[0107] A doped and modified hard carbon material and its preparation method and application. The preparation method of the doped and modified hard carbon material is as follows:

[0108] (1) The carbon source obtained by pre-carbonizing phenolic resin at 500°C for 6 hours under a nitrogen atmosphere was placed in a high-energy ball mill containing an oxygen atmosphere at a pressure of 0.8 MPa, and mechanically ball milled for 2 hours under the discharge conditions of a ball mill discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A to obtain an oxygen-doped carbon material; the rotation speed during the mechanical ball milling was 1100 r / min, and the ball-to-material ratio of the ball milling beads was 10:1;

[0109] (2) heating the oxygen-doped carbon material to 1600°C in a nitrogen atmosphere and maintaining the temperature for 20 hours to obtain a doped hard carbon precursor;

[0110] (3) The doped hard carbon material is placed in a high-energy ball mill containing an acetylene atmosphere at a pressure of 0.5 MPa without placing ball mill beads, and subjected to oscillatory vibration treatment under the discharge conditions of the ball mill at a discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A to obtain a doped modified hard carbon material; the rotation speed of the ball mill during the oscillatory vibration treatment is 1100 r / min.

[0111] Comparative Example 4

[0112] A doped and modified hard carbon material and its preparation method and application. The preparation method of the doped and modified hard carbon material is as follows:

[0113] (1) The carbon source obtained by pre-carbonizing phenolic resin at 500°C for 6 hours under a nitrogen atmosphere was placed in a high-energy ball mill containing a hydrogen sulfide atmosphere at a pressure of 0.8 MPa, and mechanically ball milled for 2 hours under the discharge conditions of a ball mill discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A to obtain a sulfur-doped carbon material; the rotation speed during the mechanical ball milling was 1100 r / min, and the ball-to-material ratio of the ball milling beads was 10:1;

[0114] (2) heating the sulfur-doped carbon material to 1600°C in a nitrogen atmosphere and maintaining the temperature for 20 hours to obtain a doped hard carbon precursor;

[0115] (3) The doped hard carbon material is placed in a high-energy ball mill containing an acetylene atmosphere at a pressure of 0.5 MPa without placing ball mill beads, and subjected to oscillatory vibration treatment under the discharge conditions of the ball mill at a discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A to obtain a doped modified hard carbon material; the rotation speed of the ball mill during the oscillatory vibration treatment is 1100 r / min.

[0116] Comparative Example 5

[0117] A doped and modified hard carbon material and its preparation method and application. The preparation method of the doped and modified hard carbon material is as follows:

[0118] (1) The carbon source obtained by pre-carbonizing phenolic resin at 500°C for 6 hours under a nitrogen atmosphere was placed in a high-energy ball mill containing a hydrogen sulfide atmosphere at a pressure of 0.8 MPa, and mechanically ball milled for 2 hours under the discharge conditions of a ball mill discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A to obtain a sulfur-doped carbon material; the rotation speed during the mechanical ball milling was 1100 r / min, and the ball-to-material ratio of the ball milling beads was 10:1;

[0119] (2) placing the sulfur-doped carbon material in a high-energy ball mill containing an oxygen atmosphere at a pressure of 0.8 MPa, and subjecting the material to mechanical ball milling for 2 h under the discharge conditions of a ball mill discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A, to obtain an oxygen-doped and sulfur-doped carbon material; the rotation speed during the mechanical ball milling treatment was 1100 r / min, and the ball-to-material ratio of the ball milling beads was 10:1;

[0120] (3) heating the oxygen-doped and sulfur-doped carbon material to 1600°C in a nitrogen atmosphere and keeping the temperature for 20 hours to obtain a doped hard carbon precursor;

[0121] (4) The doped hard carbon material is placed in a high-energy ball mill containing an acetylene atmosphere at a pressure of 0.5 MPa without placing ball mill beads, and subjected to oscillatory vibration treatment under the discharge conditions of the ball mill at a discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A to obtain a doped modified hard carbon material; the rotation speed of the ball mill during the oscillatory vibration treatment is 1100 r / min.

[0122] Comparative Example 6

[0123] A doped and modified hard carbon material and its preparation method and application. The preparation method of the doped and modified hard carbon material is as follows:

[0124] (1) The carbon source obtained by pre-carbonizing phenolic resin at 500°C for 6 hours under a nitrogen atmosphere was placed in a high-energy ball mill containing an oxygen atmosphere at a pressure of 0.8 MPa and a hydrogen sulfide atmosphere at a pressure of 0.8 MPa, and mechanically ball milled for 2 hours under the discharge conditions of a ball mill discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A to obtain a sulfur-doped and oxygen-doped carbon material; the rotation speed during the mechanical ball milling treatment was 1100 r / min, and the ball-to-material ratio of the ball milling beads was 10:1;

[0125] (2) heating the sulfur-doped and oxygen-doped carbon material to 1600°C in a nitrogen atmosphere and keeping the temperature for 20 hours to obtain a doped hard carbon precursor;

[0126] (3) The doped hard carbon material is placed in a high-energy ball mill containing an acetylene atmosphere at a pressure of 0.5 MPa without placing ball mill beads, and subjected to oscillatory vibration treatment under the discharge conditions of the ball mill at a discharge frequency of 20 kHz, a discharge voltage of 15 kV, and a discharge current of 2 A to obtain a doped modified hard carbon material; the rotation speed of the ball mill during the oscillatory vibration treatment is 1100 r / min.

[0127] Effect Example 1

[0128] In order to explore the influence of the oxygen and sulfur doping stages on the doping effect during the preparation of the doped modified hard carbon material by the preparation method described in this article, the materials of each embodiment and comparative example before the hard carbon conversion process at 1600°C and 20h were tested for oxygen atom content, sulfur atom content, and specific surface area. The results are shown in Table 1.

[0129] Table 1

[0130] Test items O content (wt%) S content (wt%) <![CDATA[Specific surface area (m 2 / g)]]> Example 1 14.4 3.2 550 Example 2 12.6 3.1 398 Example 3 16.2 2.9 683 Example 4 11.9 3.3 455 Example 5 17 3.1 622 Example 6 13 3 493 Example 7 15.5 3 601 Example 8 14.9 2.1 450 Example 9 13.8 4.5 620 Example 10 15.6 1.7 496 Example 11 13 4.9 603 Example 12 15.1 2.5 542 Example 13 13.5 4.1 557 Example 14 14.7 3.4 553 Example 15 14.4 3.2 551 Example 16 14.3 3.1 549 Example 17 14.4 3 549 Example 18 14.2 3.2 548 Example 19 14.5 3.1 550 Example 20 14.1 3.1 544 Comparative Example 1 7.3 0 234 Comparative Example 2 14.5 3.2 548 Comparative Example 3 16.7 0 389 Comparative Example 4 5.3 1.0 254 Comparative Example 5 16.9 1.0 549 Comparative Example 6 16.3 1.5 405

[0131] As can be seen from Table 1, in the oxygen-doping and sulfur-doping stages, with the extension of treatment time, the increase of discharge current and the increase of atmosphere pressure, the oxygen / sulfur doping amount in the material will increase. At the same time, due to the etching of plasma, the number of pore structures on the surface of the material increases, so the specific surface area will also increase, which can provide more sodium ion storage sites. In the oxygen-doping stage, such as Figure 1 As shown, compared with the carbon source, the oxygen-doped carbon material obtained in Example 1 introduces oxygen-containing functional groups such as carbonyl and ether bonds on the aromatic ring, which are beneficial to the subsequent reaction with sodium ions. In the sulfur-doping stage, the oxygen-doped carbon material will further introduce carbon-sulfur bonds to expand the interlayer spacing of the crystal plane. However, if the treatment time of the sulfur-doping stage increases / the discharge current increases / the atmosphere pressure increases, the oxygen content in the material may decrease. This is mainly because the carbon-oxygen bonds in the material are converted into water vapor and carbon-sulfur bonds, and the oxygen atoms are lost as water vapor is discharged. At the same time, compared with the oxygen-doping stage, the increase in the specific surface area of ​​this stage with the change of parameters is relatively small. In contrast, the specific surface area of ​​the product of Comparative Example 1, which has not undergone plasma-assisted ball milling treatment, is smaller. Among the products of Comparative Examples 3 and 4, which have only oxygen-doping or sulfur-doping stages, the specific surface area of ​​the product of Comparative Example 3 is close to that of Example 1, while the specific surface area of ​​the product of Comparative Example 4 is close to that of Comparative Example 1, indicating that the plasma etching in the sulfur-doping stage has little effect on the specific surface area of ​​the material.

[0132] It can be seen from Comparative Examples 5 and 6 that placing the oxygen doping step after sulfur doping or performing it simultaneously is not conducive to S doping, and the oxygen content on the surface of the material will increase after doping. This is because in addition to directly reacting with the carbon material to form a CS bond (C+H2S→C-S+H2), S doping also relies on the reaction of the CO bond on the surface of the material with hydrogen sulfide plasma to form a CS bond and produce water vapor (C-O+H2S→C-S+H2O). Compared with the process of oxygen doping first and then sulfur doping, placing sulfur doping before oxygen doping or performing the two steps simultaneously, there are no large numbers of CO bonds on the surface of the material to react with H2S, resulting in a decrease in S content and an increase in O content after doping.

[0133] Furthermore, the specific surface area, true density, closed pore volume, and inter-crystalline interlayer spacing of the products of each embodiment and comparative example were tested, and the results are shown in Table 2.

[0134] Table 2

[0135]

[0136]

[0137]

[0138] As shown in Table 2, the physical properties of the final product vary due to differences in process parameters during the oxygen and sulfur doping stages. With increasing treatment time, discharge current, and atmosphere pressure, the interlayer spacing and closed pore volume of the final product increase, thereby increasing the number of storage sites available for sodium ion transport. This increases the product's reversible capacity, but also its specific surface area, which reduces its initial coulombic efficiency. Furthermore, during the sulfur doping stage, these changes in conditions may lead to excessive sulfur doping, resulting in increased irreversible capacity and reduced initial coulombic efficiency. During the acetylene-based carbon source coating modification process, the thickness of the acetylene-deposited carbon layer gradually increases with increasing treatment time or discharge current / acetylene pressure. While this increases its initial coulombic efficiency, its reversible capacity decreases. Therefore, employing more appropriate process conditions throughout the overall preparation process can lead to better product performance. In comparison, the undoped product of Comparative Example 1 has a smaller interlayer spacing on the crystal plane. XRD testing of the doped hard carbon precursor obtained in step (3) of Example 1 and the product obtained in Comparative Example 1 reveals that the characteristic peak corresponding to the (002) crystal plane in the doped hard carbon precursor is shifted to the left compared to that of the product of Comparative Example 1, indicating that the interlayer spacing on the crystal plane increases under the doping of oxygen and sulfur atoms.

[0139] Effect Example 2

[0140] To investigate the electrochemical performance of the doped and modified hard carbon materials prepared by the methods described herein, button-type cells were fabricated using the products from each example and comparative example, and their initial charge specific capacity and initial coulombic efficiency were measured. The working electrode was prepared by mixing the products from each example / comparative example, conductive carbon, and sodium carboxymethyl cellulose in a mass ratio of 95:2:3 in deionized water and coating the mixture on copper foil. A sodium sheet was used as the counter electrode. The electrolyte consisted of 1 mol / L NaClO₄ dissolved in a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (EC:PC, volume ratio: 1:1) with 5 wt% FEC (fluoroethylene carbonate). Glass fiber was used as the separator. The button-type cells were assembled in a glove box maintained at oxygen and water concentrations below 1 ppm. The electrochemical performance of the cells was measured using an electrochemical workstation. The test voltage ranged from 0.01 to 2.0 V, and the current density was 30 mA / g. The test results are shown in Table 3.

[0141] Table 3

[0142]

[0143]

[0144] As can be seen from Table 3, corresponding to Table 2, due to the plasma-assisted doping of oxygen atoms and sulfur atoms, the reversible capacity of the products of Example 1 is significantly improved compared with the product of Comparative Example 1 without doping, and the charge specific capacity can reach up to 340 mAh / g. As shown in the product of Comparative Example 2, the first coulombic efficiency of the product is reduced by more than 5% compared with that of Example 1, so further carbon coating is required to suppress this phenomenon; on the other hand, the oxygen doping and sulfur doping stages need to be carried out successively, otherwise too many carbon-oxygen bonds will remain in the product and it will be unfavorable for sulfur doping, making it difficult to improve the performance of the product, as shown in Comparative Examples 5 and 6. On the other hand, it can be seen from Example 1 and Examples 8 to 13 that if the degree of sulfur doping increases, the performance of the product will also decrease, because excessive doping of sulfur atoms will cause the defect concentration in the material to increase, resulting in an increase in irreversible capacity and a decrease in the first coulombic efficiency; from the comparison of product performance between Example 1 and Examples 14 to 19, it can be seen that the thickness of the outermost modified coated carbon also needs to be considered. If it is too thin, the first coulombic efficiency of the product cannot be effectively improved, and if it is too thick, the reversible capacity of the product will be reduced.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of this article may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of this article.

Claims

1. A method for preparing a doped and modified hard carbon material, characterized in that: The following steps are involved: The pre-carbonized carbon source is placed in a ball milling device containing an oxygen atmosphere and subjected to mechanical ball milling treatment under discharge conditions to obtain an oxygen-doped carbon material; The oxygen-doped carbon material is placed in a ball milling device containing hydrogen sulfide atmosphere and subjected to mechanical ball milling treatment under discharge conditions to obtain a sulfur-doped and oxygen-doped carbon material; the sulfur-doped and oxygen-doped carbon material has an oxygen content of 11 to 17 wt%, a sulfur content of 1 to 5 wt%, and a specific surface area of ​​350 to 700 m 2 / g; The sulfur-doped and oxygen-doped carbon material is kept at 1500-1700° C. for 15-25 hours under a protective atmosphere to obtain a doped hard carbon material; placing the doped hard carbon material in a vibration device containing acetylene atmosphere and performing oscillatory vibration treatment under discharge conditions to obtain a doped modified hard carbon material; The vibration device is a high-energy ball mill without ball milling beads. When preparing doped and modified hard carbon materials, the swing vibration rate of the high-energy ball mill is 1000-1200 r / min, and the swing vibration time is 1-3 hours. When preparing doped and modified hard carbon materials, the discharge frequency of the high-energy ball mill is 15-25 kHz, the discharge voltage is 14-16 kV, and the discharge current is 1-3 A. The pressure of the acetylene atmosphere in the high-energy ball mill is 0.3-0.7 MPa.

2. The method for preparing a doped and modified hard carbon material according to claim 1, wherein: The carbon source is at least one of phenolic resin, epoxy resin, glucose and sucrose; the pre-carbonization temperature of the carbon source is 400-600° C., and the time is 4-8 hours.

3. The method for preparing a doped and modified hard carbon material according to claim 1, wherein: The ball milling device is a high-energy ball mill. When preparing oxygen-doped carbon materials, the ball milling speed of the high-energy ball mill is 1000-1200 r / min, the ball milling time is 1-3 hours, and the ball-to-material ratio is (8-12):

1.

4. The method for preparing a doped and modified hard carbon material according to claim 3, wherein: When preparing oxygen-doped carbon materials, the discharge frequency of the high-energy ball mill is 15-25 kHz, the discharge voltage is 14-16 kV, and the discharge current is 1-3 A; the pressure of the oxygen atmosphere in the high-energy ball mill is 0.6-1 MPa.

5. The method for preparing a doped and modified hard carbon material according to claim 1, wherein: The ball milling device is a high-energy ball mill. When preparing sulfur-doped and oxygen-doped carbon materials, the ball milling speed of the high-energy ball mill is 1000-1200 r / min, the ball milling time is 1-3 hours, and the ball-to-material ratio is (8-12):

1.

6. The method for preparing a doped and modified hard carbon material according to claim 5, wherein: When preparing sulfur-doped and oxygen-doped carbon materials, the discharge frequency of the high-energy ball mill is 15-25 kHz, the discharge voltage is 14-16 kV, and the discharge current is 1-3 A; the pressure of the hydrogen sulfide atmosphere in the high-energy ball mill is 0.6-1 MPa.

7. The doped and modified hard carbon material prepared by the method for preparing a doped and modified hard carbon material according to any one of claims 1 to 6, characterized in that: The specific surface area of ​​the doped modified hard carbon material is 0.6 to 9.5 m 2 / g, true density is 1.4~1.85g / cm 3 , the closed cell area is 0.08~0.28cm 3 / g, and the interlayer spacing of the crystal plane is 3.9~4.3nm.

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