Asphalt-based hard carbon material as well as preparation method and application thereof

Abstract

The invention discloses an asphalt-based hard carbon material and a preparation method and application thereof.The preparation method of the asphalt-based hard carbon material comprises the following steps that a uniformly-mixed hard carbon precursor is subjected to molecular crosslinking and surface oxidation treatment through a one-pot method, an oxidation precursor is obtained, and the hard carbon precursor comprises asphalt powder and acid ammonium ligands; and performing high-temperature carbonization on the oxidized precursor in an inert environment to obtain the asphalt-based hard carbon material. The novel asphalt-based hard carbon material is prepared through triple interference mechanisms of surface oxidation, molecular crosslinking modification and pore adjustment, and compared with traditional asphalt-based hard carbon, the sodium storage capacity of the novel asphalt-based hard carbon material is qualitatively improved. In addition, the asphalt-based hard carbon material is simple in preparation process, high in operability and low in raw material cost, and a reliable technical route is provided for large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage devices, and more particularly, to an asphalt-based hard carbon material, a preparation method thereof, and an application thereof. Background Art

[0002] Due to its unique highly disordered, nano-crystalline, and rich pore structure, hard carbon materials exhibit great application potential in applications such as sodium-ion batteries. During the preparation of traditional asphalt-based hard carbon materials, they are extremely prone to graphitization, reducing the sodium storage capacity of the materials.

[0003] In order to inhibit the graphitization process during carbonization, the asphalt precursor is usually modified by using single molecular cross-linking, template modification, heteroatom doping, or surface oxidation treatment. Although the problem of the graphitization process is alleviated to a certain extent, problems such as uneven oxidation, complex template removal process and difficulty in large-scale production, and cost increase will occur.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide an asphalt-based hard carbon material, a preparation method thereof, and an application thereof to improve the above technical problems.

[0006] The present invention is implemented as follows:

[0007] In a first aspect, the present invention provides a preparation method of an asphalt-based hard carbon material, including the following steps:

[0008] Performing molecular cross-linking and surface oxidation treatment on the uniformly mixed hard carbon precursor by a one-pot method to obtain an oxidized precursor, wherein the hard carbon precursor includes asphalt powder and ammonium acid ligands;

[0009] Performing high-temperature carbonization on the oxidized precursor in an inert environment to obtain the asphalt-based hard carbon material.

[0010] In an alternative embodiment, the ammonium acid ligands include at least one of ammonium formate, ammonium acetate, ammonium oxalate, ammonium carbonate, ammonium sulfate, and ammonium nitrate, and the ammonium acid ligand is preferably ammonium acetate;

[0011] Preferably, the dosage of the ammonium acid ligand is 40 wt% - 90 wt% of the hard carbon precursor, and preferably 65 wt% - 75 wt%.

[0012] In an alternative embodiment, the softening point of the asphalt powder is 110°C - 300°C, preferably 240°C - 260°C;

[0013] Preferably, the asphalt powder includes at least one of petroleum asphalt, coal tar pitch, and natural asphalt; the asphalt is preferably petroleum asphalt;

[0014] Preferably, the particle size of the asphalt powder is less than 300 mesh.

[0015] In an alternative embodiment, the one-pot method for molecular crosslinking and surface oxidation treatment includes: subjecting the hard carbon precursor to crosslinking treatment at a first temperature, then raising the temperature to a second temperature for preliminary surface oxidation treatment, and further raising the temperature to a third temperature for deep surface oxidation treatment.

[0016] In an alternative embodiment, the first temperature is 80°C to 150°C, and the time for the crosslinking treatment is 1 h to 8 h; the second temperature is 200°C to 290°C, the time for the preliminary surface oxidation treatment is 1 h to 10 h, the third temperature is 300°C to 400°C, and the time for the deep surface oxidation treatment is 1 h to 12 h; more preferably, the first temperature is 90°C to 110°C, the time for the crosslinking treatment is 3 h to 5 h; the second temperature is 220°C to 240°C, the time for the preliminary surface oxidation treatment is 1.5 h to 2.5 h, the third temperature is 340°C to 360°C, and the time for the deep surface oxidation treatment is 5 h to 7 h;

[0017] Preferably, the molecular crosslinking and surface oxidation treatment are carried out in a heating furnace body, and an oxygen-containing gas is continuously introduced into the heating furnace body during the preliminary surface oxidation treatment and the deep surface oxidation treatment. Preferably, the oxygen-containing gas is air.

[0018] In an alternative embodiment, the temperature of the high-temperature carbonization is 1000°C to 1600°C, and the time for the high-temperature carbonization is 1 h to 6 h;

[0019] Preferably, the temperature of the high-temperature carbonization is 1200°C to 1400°C, and the time for the high-temperature carbonization is 2 h to 4 h.

[0020] In an alternative embodiment, the inert environment is an inert atmosphere. Preferably, the gas of the inert atmosphere is composed of one or more of nitrogen, helium, neon, and argon, and more preferably nitrogen.

[0021] In a second aspect, the present invention provides an asphalt-based hard carbon material prepared by the preparation method according to any one of the foregoing embodiments. Preferably, a 2016-type simulated battery assembled with the asphalt-based hard carbon material as the working electrode and metallic sodium as the counter electrode has a reversible specific capacity greater than 300 mAh / g and a first Coulombic efficiency greater than 89% when cycled at a current density of 0.1 C for 70 cycles.

[0022] In a third aspect, the present invention provides an application of the asphalt-based hard carbon material as described in the foregoing embodiment in the preparation of energy storage devices.

[0023] Fourthly, the present invention provides an energy storage device, which includes a working electrode, and the raw material of the working electrode includes the pitch-based hard carbon material as described in the foregoing embodiments.

[0024] The present invention has the following beneficial effects: A novel pitch-based hard carbon material is prepared through a triple interference mechanism of surface oxidation, molecular crosslinking modification, and pore regulation. First, ammonium acid ligands are introduced in the surface oxidation stage, and surface oxidation and molecular crosslinking are carried out simultaneously at the molecular level. Based on the synergistic effect of the two, the highly disordered and nano-crystalline structure of the material can be effectively regulated. Secondly, the gas generated by the decomposition of ammonium acid ligands can effectively regulate the pore structure of the material. The novel pitch-based hard carbon material regulated by the triple interference mechanism has a qualitative improvement in sodium storage capacity compared with the traditional pitch-based hard carbon. In addition, the preparation process of this pitch-based hard carbon material is simple, highly operable, and has a low raw material cost, providing a reliable technical route for large-scale production. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0026] Figure 1 、 Figure 2 is the SEM image of the pitch-based hard carbon material of Example 1 of the present invention;

[0027] Figure 3 is the first charge-discharge curve graph of the pitch-based hard carbon materials of Examples 1-3 of the present invention;

[0028] Figure 4 is the comparison graph of the first charge-discharge of the pitch-based hard carbon materials of Examples 9 and 10 of the present invention;

[0029] Figure 5 is the cycle performance graph of the pitch-based hard carbon material of Example 1 of the present invention;

[0030] Figure 6 is the compaction curve graph of the pitch-based hard carbon materials of Examples 1, 10 and Comparative Example 1 of the present invention;

[0031] Figure 7 is the conductivity graph of the pitch-based hard carbon materials of Examples 1, 10 and Comparative Example 1 of the present invention. Detailed Embodiments

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0033] The following specifically describes an asphalt-based hard carbon material provided by the present invention, its preparation method, and applications.

[0034] Some embodiments of the present invention provide a method for preparing an asphalt-based hard carbon material, including the following steps: performing molecular cross-linking and surface oxidation treatment on the uniformly mixed hard carbon precursor by a one-pot method to obtain an oxidized precursor, wherein the hard carbon precursor includes asphalt powder and ammonium acid ligands; performing high-temperature carbonization on the oxidized precursor in an inert environment to obtain the asphalt-based hard carbon material.

[0035] Through a large amount of research and practice, the inventors found that the sodium storage capacity of asphalt-based hard carbon can be significantly improved through a triple interference mechanism of surface oxidation, molecular cross-linking modification, and pore regulation. By introducing ammonium acid ligands in the surface oxidation stage, surface oxidation and molecular cross-linking are carried out simultaneously at the molecular level. Based on the synergistic effect of the two, the highly disordered and nano-crystalline structure of the material can be effectively regulated. Secondly, the gas generated by the decomposition of ammonium acid ligands can effectively regulate the pore structure of the material. The preparation process of this asphalt-based hard carbon material is simple, highly operable, and has a low raw material cost, providing a reliable technical route for large-scale production.

[0036] In some embodiments, the method for preparing the asphalt-based hard carbon material includes the following steps:

[0037] S1. Prepare the hard carbon precursor.

[0038] Specifically, take a certain amount of asphalt and crush it in a crusher. After crushing, pass it through a 300-mesh sieve to obtain asphalt powder, and mix the asphalt powder with ammonium acid ligands in different mass ratios.

[0039] Exemplarily, the ammonium acid ligands include at least one of ammonium formate, ammonium acetate, ammonium oxalate, ammonium carbonate, ammonium sulfate, and ammonium nitrate, and the ammonium acid ligand is preferably ammonium acetate. For reference, in order to achieve better molecular cross-linking and surface oxidation effects, the dosage of the ammonium acid ligand is 40 wt% - 90 wt% of the hard carbon precursor, such as 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, or 90 wt%, etc., and preferably 65 wt% - 75 wt%.

[0040] In order to enable asphalt to cooperate well with ammonium acid ligands for molecular cross-linking and surface oxidation, and to facilitate the formation of a uniform pore structure, in some embodiments, asphalt powder with a relatively low softening point is selected. Exemplarily, the softening point of the asphalt powder is 110°C to 300°C, such as 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, 235°C, 240°C, 245°C, 250°C, 255°C, 260°C, 265°C, 270°C, 275°C, 280°C, 285°C, 290°C or 300°C, etc., or between any two of the above temperatures, preferably 240°C to 260°C.

[0041] For reference, the asphalt powder includes at least one of petroleum asphalt, coal tar asphalt, and natural asphalt. Exemplarily, the asphalt can be selected as petroleum asphalt.

[0042] It should be noted that the particle size of the asphalt powder is less than 300 mesh, which is more conducive to the uniform dispersion and cross-linking performance of the asphalt in the molten state.

[0043] S2. Subject the uniformly mixed hard carbon precursor to molecular cross-linking and surface oxidation treatment by the one-pot method to obtain an oxidized precursor.

[0044] Specifically, in some embodiments, the molecular cross-linking and surface oxidation treatment by the one-pot method includes: subjecting the hard carbon precursor to cross-linking treatment at a first temperature, then raising the temperature to a second temperature for preliminary surface oxidation treatment, and then raising the temperature to a third temperature for deep surface oxidation treatment.

[0045] Exemplarily, in some embodiments, the first temperature is 80°C to 150°C, such as 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C, etc., the crosslinking treatment time is 1 h to 8 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h, etc.; the second temperature is 200°C to 290°C, such as 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C or 290°C, etc., the surface preliminary oxidation treatment time is 1 h to 10 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc., the third temperature is 300°C to 400°C, such as 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C or 400°C, etc., the surface deep oxidation treatment time is 1 h to 12 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h or 12 h, etc.

[0046] To further optimize the effects of crosslinking and surface oxidation treatment, in some embodiments, the first temperature is 90°C to 110°C, the crosslinking treatment time is 3 h to 5 h; the second temperature is 220°C to 240°C, the surface preliminary oxidation treatment time is 1.5 h to 2.5 h, the third temperature is 340°C to 360°C, the surface deep oxidation treatment time is 5 h to 7 h.

[0047] In some embodiments, the molecular crosslinking and surface oxidation treatment are carried out in a heating furnace body, and an oxygen-containing gas is continuously introduced into the heating furnace body during the surface preliminary oxidation treatment and the surface deep oxidation treatment. Preferably, the oxygen-containing gas is air. Exemplarily, the heating furnace body can be selected as a muffle furnace.

[0048] S3. High-temperature carbonize the oxidation precursor in an inert environment to obtain a pitch-based hard carbon material.

[0049] Specifically, in some embodiments, the temperature of high-temperature carbonization is 1000°C to 1600°C, such as 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, 1500°C, 1550°C or 1600°C, etc., or between any two of the above temperatures, and the time of high-temperature carbonization is 1 h to 6 h, such as 1 h, 2 h, 3 h, 4 h, 5 h or 6 h, etc.

[0050] Further optimizing the conditions of high-temperature carbonization, the temperature of high-temperature carbonization can be selected as 1200°C to 1400°C, and the time of high-temperature carbonization can be selected as 2 h to 4 h.

[0051] In some embodiments, in order to avoid the reaction between the carbon material and oxygen during the high-temperature carbonization process, which may cause a decrease in the quality of the carbon material, the inert environment is an inert atmosphere. Preferably, the gas of the inert atmosphere is composed of one or more of nitrogen, helium, neon, and argon, and more preferably nitrogen.

[0052] Some embodiments of the present invention also provide an asphalt-based hard carbon material, which is prepared by the preparation method described in any one of the foregoing embodiments. Using this asphalt-based hard carbon material as the working electrode and metallic sodium as the counter electrode, the 2016-type simulated battery is cycled 70 times at a current density of 0.1C, and the reversible specific capacity is greater than 300 mAh / g, and the initial Coulombic efficiency is greater than 89%.

[0053] Some embodiments of the present invention also provide the application of the asphalt-based hard carbon material as described in the foregoing embodiments in the preparation of energy storage devices.

[0054] Some embodiments of the present invention also provide an energy storage device, which includes a working electrode, and the raw material of the working electrode includes the asphalt-based hard carbon material as described in the foregoing embodiments.

[0055] The features and properties of the present invention will be further described in detail below in conjunction with examples.

[0056] Example 1

[0057] This example provides a preparation method of an asphalt-based hard carbon material, which specifically includes the following steps:

[0058] The petroleum asphalt with a softening point of 250°C is crushed by a crusher and then passed through a 300-mesh sieve. The mass fraction of the ammonium acetate ligand is 70% of the mixture. After mixing evenly, it is placed in a muffle furnace for surface oxidation and molecular cross-linking. First, it is heated from room temperature to 100°C for oxidation for 4 h, then the air flow rate is adjusted to 1 L / min and kept stable, then heated to 230°C for oxidation for 2 h, and finally heated to 350°C for oxidation for 6 h to obtain a precursor material.

[0059] After the precursor is cooled to room temperature, it is finely ground into a uniform powder using an agate mortar and then placed in a tubular furnace for carbonization. Under a nitrogen atmosphere, at a heating rate of 2°C / min, it is heated to 1300°C and held for 3 h to obtain the asphalt-based hard carbon material.

[0060] The morphology and structure of the material were collected using a scanning electron microscope, as shown in Figure 1 and Figure 2 It can be seen from Figure 1-2 that the hard carbon material presents an irregular block shape, and the surface is rough with abundant macropores, which can effectively increase the contact area with the electrolyte and shorten the ion migration distance.

[0061] Example 2

[0062] This example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 1, except that the mass fraction of the ammonium acetate ligand is 60%.

[0063] Example 3

[0064] This example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 1, except that the mass fraction of the ammonium acetate ligand is 80%.

[0065] Example 4

[0066] This example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 1. The difference lies only in the surface oxidation and molecular cross-linking process: after heating from room temperature to 100 °C and oxidizing for 4 h, the air flow rate is adjusted to 1 L / min and kept stable, then heated to 260 °C and oxidized for 2 h, and finally heated to 350 °C and oxidized for 6 h to obtain a precursor material.

[0067] Example 5

[0068] This example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 1. The difference lies only in the surface oxidation and molecular cross-linking process: after heating from room temperature to 100 °C and oxidizing for 4 h, the air flow rate is adjusted to 1 L / min and kept stable, then heated to 230 °C and oxidized for 2 h, and finally heated to 330 °C and oxidized for 6 h to obtain a precursor material.

[0069] Example 6

[0070] This example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 1. The difference lies only in the surface oxidation and molecular cross-linking process: after heating from room temperature to 100 °C and oxidizing for 4 h, the air flow rate is adjusted to 1 L / min and kept stable, then heated to 230 °C and oxidized for 2 h, and finally heated to 370 °C and oxidized for 6 h to obtain a precursor material.

[0071] Example 7

[0072] This example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 1. The difference lies only in the carbonization process: in a nitrogen atmosphere, at a heating rate of 2 °C / min, heated to 1200 °C and kept for 3 h to obtain a new type of asphalt-based hard carbon material.

[0073] Example 8

[0074] This example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 1, except that the carbonization process is as follows: under a nitrogen atmosphere, with a heating rate of 2 °C / min, heat to 1400 °C and hold for 3 h to obtain a new type of asphalt-based hard carbon material.

[0075] Example 9

[0076] This example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 1, except that the ligand is replaced with ammonium formate instead of ammonium acetate.

[0077] Example 10

[0078] This example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 2, except that the ligand is replaced with ammonium formate instead of ammonium acetate.

[0079] Comparative Example 1

[0080] This comparative example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 1, except that: no ammonium acid ligand is added.

[0081] Comparative Example 2

[0082] This comparative example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 4, except that: no ammonium acid ligand is added.

[0083] Comparative Example 3

[0084] This comparative example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 5, except that: no ammonium acid ligand is added.

[0085] No ammonium acid ligand is added.

[0086] Comparative Example 4

[0087] This comparative example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps in Example 6, except that: no ammonium acid ligand is added.

[0088] Comparative Example 5

[0089] This comparative example provides a method for preparing an asphalt-based hard carbon material, which places petroleum asphalt powder with a softening point of 250 °C in a tubular furnace for carbonization. Under a nitrogen atmosphere, with a heating rate of 2 °C / min, heat to 1300 °C and hold for 3 h to obtain an asphalt-based hard carbon material.

[0090] Comparative Example 6

[0091] This comparative example provides a method for preparing an asphalt-based hard carbon material, which is basically the same as the steps of Example 1, except that: surface oxidation and molecular crosslinking are not carried out, and it is directly placed in a tubular furnace for carbonization. Under a nitrogen atmosphere, it is heated to 1300 °C at a heating rate of 2 °C / min and kept warm for 3 h to obtain the asphalt-based hard carbon material.

[0092] Taking the asphalt-based hard carbon materials prepared in Examples 1 to 10 and Comparative Examples 1 to 6 as examples, using metallic sodium as the counter electrode, and using the asphalt-based hard carbon materials obtained in each example and comparative example as the working electrode, 2016-type simulated batteries are assembled respectively. The simulated batteries are placed in a blue electrochemical test system, the voltage range is set to 0 - 2.5 V, the current density 1C = 300 mA / g, and the charge-discharge test is carried out at a rate of 0.1C to verify the sodium storage performance of the materials.

[0093] The reversible specific capacity and the first Coulombic efficiency are shown in Table 1.

[0094] Table 1

[0095] Example Reversible specific capacity (mAh / g) Initial Coulombic efficiency Example 1 338 89.47％ Example 2 267 86.09％ Example 3 296 87.64％ Example 4 335 89.75％ Example 5 328 89.18％ Example 6 320 87.40％ Example 7 316 87.41％ Example 8 329 90.07％ Example 9 308 89.83％ Example 10 327 89.54％ Comparative Example 1 239 84.67％ Comparative Example 2 217 83.01％ Comparative Example 3 263 87.36％ Comparative Example 4 216 86.17％ Comparative Example 5 88.1 62.21％ Comparative Example 6 90.4 61.4％

[0096] Analyzing Table 1 and comparing Examples 1, 10 with Comparative Example 1, it can be seen that compared with the single surface oxidation intervention mechanism, introducing ammonium acid ligands can increase the reversible specific capacity by 41% and raise the first Coulombic efficiency to over 89%. This fully shows that introducing ammonium acid ligands can effectively promote the molecular crosslinking of asphalt. Through the triple mechanisms of surface oxidation, molecular crosslinking, and pore regulation, the graphitization process is thoroughly inhibited, making the finally obtained hard carbon material have an ultra-high reversible specific capacity and first efficiency.

[0097] It is not difficult to find from Examples 1 - 3 and 9 - 10 that the ratio of the ligand to the main material has a profound influence on the regulation of the material. This is mainly because there is a certain threshold for the degree of crosslinking, and too high a degree of crosslinking will have a negative effect.

[0098] Comparing Examples 1 - 8 and Comparative Examples 1 - 4, it is not difficult to find that the temperature and time of surface oxidation and the temperature and time of molecular crosslinking are crucial for the regulation of the material. First, for the crosslinking temperature and time, if the crosslinking temperature is too high, the ligand will denature and the degree of crosslinking will decrease; if the crosslinking time is too long, the degree of crosslinking will exceed the threshold and affect the performance of the material. Second, the same is true for the temperature and time of surface oxidation. Too high a temperature or too long a time will introduce a large number of heteroatoms (such as oxygen molecules, etc.), which will directly cause changes in the surface chemical composition of the material and thus affect the electrochemical behavior of the material. Moreover, the material is particularly sensitive to the final carbonization temperature. Too high a temperature will remove too many heteroatoms and accelerate the graphitization process; too low a temperature will result in insufficient graphitization degree of the material, which is also not conducive to the exertion of electrochemical ability.

[0099] The first-cycle charge-discharge curves of Examples 1 - 3 are asFigure 3 As shown by Figure 3 it can be found that the sodium storage capacity first increases and then decreases with the increase of the ligand. It is speculated that this may be related to the degree of molecular crosslinking. Further, it shows that an appropriate crosslinking degree is also crucial for the regulation of material properties.

[0100] The first charge-discharge curves of Example 9 and Example 10 are as Figure 4 shown by Figure 4 it can be found that even if the ligand is replaced, the sodium storage capacity still has a qualitative improvement. This fully reflects the universality of the ligand, and at the same time, it can be speculated that the ammonium component in the ligand plays a dominant role.

[0101] The pitch-based hard carbon material of Example 1 has an ideal cycle life, and its cycle performance graph is as Figure 5 shown. At a current density of 0.1C, it still maintains a specific capacity of more than 307 mAh / g after 70 cycles, and the capacity retention rate exceeds 90%.

[0102] Furthermore, the powder conductivity meter was used to collect the compaction density and conductivity of the hard carbon materials of Example 1, Example 10 and Comparative Example 1 ( Figure 6 - Figure 7 ). It is not difficult to find that the conductivity and compaction density of Example 1 and Example 10 are slightly lower than those of Comparative Example 1, which is mainly due to the influence of pore regulation and the high graphitization degree of the material. This also indirectly reflects that the triple intervention mechanism of surface oxidation, molecular crosslinking and pore regulation is effective.

[0103] In summary, the embodiments of the present invention prepare a new type of pitch-based hard carbon material through a triple interference mechanism of surface oxidation, molecular crosslinking modification and pore regulation. First, ammonium acid ligands are introduced in the surface oxidation stage, and surface oxidation and molecular crosslinking are carried out simultaneously at the molecular level. Based on the synergistic effect of the two, the highly disordered and nano-crystalline structure of the material can be effectively regulated. Secondly, the gas generated by the decomposition of the ammonium acid ligand can effectively regulate the pore structure of the material. After verification, the reversible specific capacity of the pitch-based hard carbon material regulated by the triple intervention mechanism can exceed 330 mAh / g, and the first Coulomb efficiency can be above 89%. There is a qualitative improvement in the sodium storage capacity compared with traditional pitch-based hard carbon. In addition, the preparation process of this pitch-based hard carbon material is simple, highly operable, and has a low raw material cost, providing a reliable technical route for large-scale production.

[0104] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of an asphalt-based hard carbon material, characterized in that It includes the following steps: The uniformly mixed hard carbon precursor is subjected to molecular crosslinking and surface oxidation treatment by a one-pot method to obtain an oxidized precursor, wherein the hard carbon precursor includes asphalt powder and ammonium acid ligands; The oxidized precursor is subjected to high-temperature carbonization in an inert environment to obtain the asphalt-based hard carbon material.

2. The preparation method according to claim 1, wherein, The ammonium acid ligands include at least one of ammonium formate, ammonium acetate, ammonium oxalate, ammonium carbonate, ammonium sulfate, and ammonium nitrate, and the ammonium acid ligand is preferably ammonium acetate; Preferably, the dosage of the ammonium acid ligand is 40 wt% - 90 wt% of the hard carbon precursor, preferably 65 wt% - 75 wt%.

3. The preparation method according to claim 1, characterized in that, The softening point of the asphalt powder is 110°C - 300°C, preferably 240°C - 260°C; Preferably, the asphalt powder includes at least one of petroleum asphalt, coal tar asphalt, and natural asphalt; the asphalt is preferably petroleum asphalt; Preferably, the particle size of the asphalt powder is less than 300 mesh.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The molecular crosslinking and surface oxidation treatment by a one-pot method includes: crosslinking the hard carbon precursor at a first temperature, then raising the temperature to a second temperature for preliminary surface oxidation treatment, and then raising the temperature to a third temperature for deep surface oxidation treatment.

5. The preparation method according to claim 4, characterized in that, The first temperature is 80°C - 150°C, and the crosslinking treatment time is 1 h - 8 h; the second temperature is 200°C - 290°C, the preliminary surface oxidation treatment time is 1 h - 10 h, the third temperature is 300°C - 400°C, and the deep surface oxidation treatment time is 1 h - 12 h; more preferably, the first temperature is 90°C - 110°C, the crosslinking treatment time is 3 h - 5 h; the second temperature is 220°C - 240°C, the preliminary surface oxidation treatment time is 1.5 h - 2.5 h, the third temperature is 340°C - 360°C, and the deep surface oxidation treatment time is 5 h - 7 h; Preferably, the molecular crosslinking and surface oxidation treatment are carried out in a heating furnace body, and an oxygen-containing gas is continuously introduced into the heating furnace body during the preliminary surface oxidation treatment and the deep surface oxidation treatment. Preferably, the oxygen-containing gas is air.

6. The preparation method according to any one of claims 1 to 3, characterized in that, The temperature of the high-temperature carbonization is 1000°C - 1600°C, and the time of the high-temperature carbonization is 1 h - 6 h; Preferably, the temperature of the high-temperature carbonization is 1200°C - 1400°C, and the time of the high-temperature carbonization is 2 h - 4 h.

7. The preparation method according to any one of claims 1 to 3, characterized in that, The inert environment is an inert atmosphere. Preferably, the gas of the inert atmosphere is composed of one or more of nitrogen, helium, neon, and argon, and more preferably nitrogen.

8. An asphalt-based hard carbon material, characterized in that, It is prepared by the preparation method according to any one of claims 1 - 7. Preferably, a 2016-type simulated battery assembled with the asphalt-based hard carbon material as the working electrode and metallic sodium as the counter electrode has a reversible specific capacity greater than 300 mAh / g and a first Coulombic efficiency greater than 89% when cycled at a current density of 0.1C for 70 cycles.

9. The application of the asphalt-based hard carbon material according to claim 8 in the preparation of energy storage devices.

10. A energy storage device, characterized in that, It includes a working electrode, and the raw material of the working electrode includes the asphalt-based hard carbon material according to claim 8.

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