Method for preparing hard carbon material through asphalt oxidation and application of hard carbon material

Abstract

The invention relates to the technical field of hard carbon materials, in particular to a hard carbon material and a preparation method and application thereof. The invention provides a preparation method of a hard carbon material, which comprises the following steps: pre-oxidizing coal pitch to obtain oxidized pitch; mixing the oxidized asphalt with a metal compound with oxidizability to obtain a mixture; sequentially carrying out pre-calcination and acid pickling on the mixture to obtain a precursor; and calcining the precursor to obtain the hard carbon material, the metal compound with oxidizing property comprises a metal salt with oxidizing property and / or a metal oxide with oxidizing property. According to the preparation method, deep oxidation of a molecular level can be realized, and the prepared hard carbon material has an excellent pore structure and electrochemical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hard carbon material, and particularly relates to a method for preparing hard carbon material by oxidizing pitch and application thereof. BACKGROUND

[0002] Pitch is a mixture of various aromatic hydrocarbons, and pre-oxidation treatment has been proved to be a common strategy for modifying pitch to build hard carbon material for sodium storage, which can prevent the melting and rearrangement of carbon structure in the subsequent carbonization process. The introduction of oxygen functional groups can control the cross-linking and polymerization of the basic structural units inside the pitch. With the increase of temperature, the cross-linked structure formed by different oxygen functional groups will undergo a solid pyrolysis process, while releasing small molecules such as carbon dioxide, avoiding the rearrangement of carbon layers in the carbonization process. However, simple air pre-oxidation method is difficult to achieve deep oxidation at the molecular level. SUMMARY

[0003] Therefore, the present application aims to provide a method for preparing hard carbon material by oxidizing pitch and application thereof, which can achieve deep oxidation at the molecular level, and the prepared hard carbon material has excellent pore structure and electrochemical performance.

[0004] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions: The present application provides a method for preparing hard carbon material, comprising the following steps: Pre-oxidizing coal pitch to obtain oxidized pitch; Mixing the oxidized pitch and metal compound with oxidizing property to obtain a mixture; Pre-calcining and acid washing the mixture in sequence to obtain a precursor; Calcining the precursor to obtain the hard carbon material; The metal compound with oxidizing property comprises metal salt with oxidizing property and / or metal oxide with oxidizing property.

[0005] Preferably, the pre-oxidation temperature is 200-400 DEG C, the time is 2-4 h, and the temperature rising rate for rising to the pre-oxidation temperature is 1-3 DEG C / min.

[0006] Preferably, the metal salt with oxidizing property comprises iron nitrate and / or magnesium nitrate; The metal oxide with oxidizing property comprises copper oxide and / or cuprous oxide.

[0007] Preferably, the mass ratio of the oxidized pitch and the metal compound with oxidizing property is (2-4):1.

[0008] Preferably, the pre-calcination temperature is 200-400 DEG C, the time is 0.5-2h, and the temperature rising rate to the pre-calcination temperature is 1-3 DEG C / min.

[0009] Preferably, the concentration of the acid solution used in the acid pickling is 3-6 mol / L. The acid solution is nitric acid solution and / or hydrochloric acid solution.

[0010] Preferably, the calcination temperature is 1200-1400 DEG C, the time is 1-3h, and the temperature rising rate to the calcination temperature is 1-3 DEG C / min.

[0011] The application further provides the hard carbon material prepared by the preparation method.

[0012] The application further provides the application of the hard carbon material in sodium ion batteries.

[0013] The application provides a preparation method of a hard carbon material, comprising the following steps: pre-oxidizing coal pitch to obtain oxidized pitch; mixing the oxidized pitch and a metal compound with oxidizability to obtain a mixture; sequentially pre-calcinating and acid pickling the mixture to obtain a precursor; and calcining the precursor to obtain the hard carbon material; and the metal compound with oxidizability comprises a metal salt with oxidizability and / or a metal oxide with oxidizability. For traditional addition of an activating agent (for example, potassium hydroxide), the addition of the activating agent mainly adopts a chemical etching mode to chemically react with carbon, leaving a large number of open pore structures and a very high specific surface area, and it is difficult to adjust the pore size in the subsequent carbonization process, and it is difficult to form a suitable closed pore structure. The preparation method provided by the application takes the oxidized pitch as a precursor, introduces the metal salt with oxidizability, and decomposes into a metal oxide and oxygen through pre-calcination, thereby simultaneously realizing double regulation of oxidation and structure: on the one hand, the oxygen generated by the decomposition promotes the internal oxidation of pitch molecules, increases the content of oxygen functional groups, and hinders the ordered growth of carbon layers in the pyrolysis process; on the other hand, the metal oxide generated as a template agent can effectively regulate the pore structure and promote the conversion of open pores to closed pores in the carbonization process, thereby realizing the synergistic optimization of carbon layer structure and micropore evolution; the metal oxide with oxidizability is introduced to realize the internal oxidation of pitch molecules through the oxidation-reduction reaction of the metal oxide with pitch; and the remaining metal oxide and metal element act as a template agent to form a pore structure. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 TG curves of M-300 and M300-FN31 in a nitrogen atmosphere; Figure 2XPS survey spectra of M300, M300-FN21, M300-FN31 and M300-FN41 (a), high resolution O 1s spectra of M300 (b) and M300-FN31 (c), and fitted oxygen-containing functional group area column charts of M300 and M300-FN31 based on high resolution O 1s spectra; Figure 3 XRD spectra of M300-1400, M300-FN21-1400, M300-FN31-1400 and M300-FN41-1400 (a), fitted peaks of (002) diffraction peak of M300-1400 (b), fitted peaks of (002) diffraction peak of M300-FN21-1400 (c), fitted peaks of (002) diffraction peak of M300-FN31-1400 (d) and fitted peaks of (002) diffraction peak of M300-FN41-1400 (e); Figure 4 Raman fitting spectra of M300-1400, M300-FN21-1400, M300-FN31-1400 and M300-FN41-1400; Figure 5 N2 adsorption / desorption curves (a), pore size distribution (b), small angle X-ray extension (SAXS, c) and true density (d) of M300-1400 and M300-FN31-1400; Figure 6 SEM images of M300-1400 (a), M300-FN21-1400 (b), M300-FN31-1400 (c) and M300-FN41-1400 (d); Figure 7 HRTEM images of M300-1400 (a), M300-FN21-1400 (b), M300-FN31-1400 (c) and M300-FN41-1400 (d); Figure 8 First cycle charge / discharge curves (a) and slope capacity and plateau capacity contributions in the second cycle discharge curve (b) of sodium-ion button cells assembled from M300-1400, M300-FN21-1400, M300-FN31-1400 and M300-FN41-1400; Figure 9 First cycle charge / discharge curves of sodium-ion button cells assembled from M200-FN31-1400, M300-FN31-1400 and M400-FN31-1400; Figure 10First charge-discharge curves of sodium-ion button batteries assembled from M300-FN31(200)-1400, M300-FN31-1400 and M300-FN31(400)-1400; Figure 11 First charge-discharge curves of sodium-ion button batteries assembled from M300-FN31-1200, M300-FN31-1300 and M300-FN31-1400; Figure 12 Sodium-ion button cells assembled from M300-1400, M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400 achieve a voltage of 0.2 mV·s. -1 CV curves at scan rates; Figure 13 Sodium-ion button cells assembled from M300-1400, M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400 have an efficiency of 0.03~1 A·g. -1 Rate performance (a), impedance curves (b), and current density at different current densities (30 mA·g) -1 Cyclic stability curve (c) is shown below. Figure 14 The CV curves (a) of the sodium-ion button cell assembled by M300-FN31-140 at different scan rates, the relationship between log(i) and log(v), and the corresponding linear fit (b). Detailed Implementation

[0015] This invention provides a method for preparing hard carbon materials, comprising the following steps: Coal tar pitch is pre-oxidized to obtain oxidized pitch; The oxidized asphalt and an oxidizing metal compound are mixed to obtain a mixture; The mixture was subjected to pre-calcination and acid washing in sequence to obtain a precursor; The precursor is calcined to obtain the hard carbon material; The oxidizing metal compounds include oxidizing metal salts and / or oxidizing metal oxides.

[0016] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0017] This invention pre-oxidizes coal tar pitch to obtain oxidized pitch.

[0018] In this invention, the pre-oxidation temperature is preferably 200~400℃, more preferably 200℃, 250℃, 300℃, 350℃ or 400℃; the time is preferably 2~4h, more preferably 2h, 2.5h, 3h, 3.5h or 4h; the heating rate to the pre-oxidation temperature is preferably 1~3℃ / min, more preferably 1℃ / min, 2℃ / min or 3℃ / min. In an embodiment of this invention, the pre-oxidation temperature can be 200℃, 300℃ or 400℃, the time can be 3h, and the heating rate to the pre-oxidation temperature can be 2℃ / min.

[0019] After obtaining the oxidized asphalt, the present invention mixes the oxidized asphalt with an oxidizing metal compound to obtain a mixture.

[0020] In this invention, the oxidizing metal salt preferably includes ferric nitrate and / or magnesium nitrate; the oxidizing metal oxide preferably includes copper oxide and / or cuprous oxide; and the oxidizing metal compound is more preferably ferric nitrate. When the oxidizing metal compound is two or more of the above-mentioned specific selections, this invention does not impose any special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. In an embodiment of this invention, the oxidizing metal compound can be ferric nitrate.

[0021] In this invention, the preferred mass ratio of the oxidized asphalt to the oxidizing metal compound is (2-4):1, more preferably 2:1, 2.5:1, 3:1, 3.5:1, or 4:1. In embodiments of this invention, the mass ratio of the oxidized asphalt to the oxidizing metal compound can be 2:1, 3:1, or 4:1.

[0022] In this invention, the preferred mixing method is ball milling. The ball milling process is not specifically limited and can be performed using a process well-known to those skilled in the art. In an embodiment of this invention, the ball milling time is specifically 2 hours.

[0023] After obtaining the mixture, the present invention sequentially pre-calcines and acid washes the mixture to obtain a precursor.

[0024] In this invention, the pre-calcination temperature is preferably 200~400℃, more preferably 200℃, 250℃, 300℃, 350℃ or 400℃; the time is preferably 0.5~2h, more preferably 0.5h, 1h, 1.5h or 2h; the heating rate to the pre-calcination temperature is preferably 1~3℃ / min, more preferably 1℃ / min, 2℃ / min or 3℃ / min. In an embodiment of this invention, the pre-calcination temperature can be 300℃, the time can be 1h, and the heating rate to the pre-calcination temperature can be 2℃ / min.

[0025] In this invention, the concentration of the acid solution used for pickling is preferably 3-6 mol / L, more preferably 3 mol / L, 4 mol / L, 5 mol / L, or 6 mol / L; the acid solution is preferably a nitric acid solution and / or a hydrochloric acid solution, more preferably a nitric acid solution. In an embodiment of this invention, the acid solution is specifically a nitric acid solution with a concentration of 4.8 mol / L. This invention does not impose any special limitations on the pickling process; any process well-known to those skilled in the art can be used.

[0026] After the acid washing is completed, the present invention preferably includes sequential water washing and drying; the water washing is preferably performed by vacuum filtration with water. The present invention has no special limitations on the vacuum filtration process, and any process well known to those skilled in the art can be used to ensure that the pH value of the sample after water washing is neutral. In the present invention, the drying method is preferably oven drying, and the drying temperature is preferably 60°C. The present invention has no special limitations on the drying time, and any time well known to those skilled in the art can be used.

[0027] After obtaining the precursor, the present invention calcines the precursor to obtain the hard carbon material.

[0028] In this invention, the calcination is preferably carried out in a protective atmosphere, preferably an argon atmosphere; the calcination temperature is preferably 1200~1400℃, more preferably 1200℃, 1250℃, 1300℃, 1350℃ or 1400℃; the time is preferably 1~3h, more preferably 1h, 1.5h, 2h, 2.5h or 3h; the heating rate to the calcination temperature is preferably 1~3℃ / min, more preferably 1℃ / min, 2℃ / min or 3℃ / min. In an embodiment of this invention, the calcination temperature can be 1400℃, the time can be 2h, and the heating rate can be 2℃ / min.

[0029] The present invention also provides a hard carbon material prepared by the preparation method described in the above technical solution.

[0030] This invention also provides the application of the hard carbon material described in the above technical solution in sodium-ion batteries. This invention does not impose any special limitations on the method of application; any method well-known to those skilled in the art can be used.

[0031] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] Example 1 1g of coal tar pitch was pre-oxidized in a muffle furnace at 300℃ for 3h at a heating rate of 2℃ / min to obtain oxidized pitch (denoted as M-300). Oxidized asphalt and ferric nitrate were ball-milled and mixed for 2 hours at a mass ratio of 3:1 to obtain a mixture. The mixture was pre-calcined (argon atmosphere, 300℃, 1h, heating rate of 2℃ / min), then acid-washed with 4.8 mol / L nitric acid solution for 3h, filtered with water until the pH of the solution was neutral, and the filter residue obtained by filtration was dried in an oven at 60℃ to obtain the precursor (denoted as M300-FN31). The precursor was calcined in a tube furnace (argon atmosphere, 1400℃, 2h, heating rate of 2℃ / min) to obtain hard carbon material (denoted as M300-FN31-1400). Figure 1 The TG curves of M-300 and M300-FN31 in a nitrogen atmosphere are given by... Figure 1 It can be seen that the carbon yields of M-300 and M300-FN31 when heated to 800℃ are 46.92% and 63.84%, respectively.

[0033] Example 2 Referring to Example 1, the difference is that the mass ratio of oxidized asphalt to ferric nitrate is 2:1, the resulting precursor is denoted as M300-FN21, and the resulting hard carbon material is denoted as M300-FN21-1400.

[0034] Example 3 Referring to Example 1, the difference is that the mass ratio of oxidized asphalt to ferric nitrate is 4:1, the resulting precursor is denoted as M300-FN41, and the resulting hard carbon material is denoted as M300-FN41-1400.

[0035] Figure 2XPS full spectra (a), high-resolution O1s spectra ((b) for M300, (c) for M300-FN31), and M300-FN41 (M300-FN21, M300-FN31, and M300-FN41) are presented, along with histograms of oxygen-containing functional group areas for M300 and M300-FN31 based on their high-resolution O1s spectra. Figure 2 The XPS full spectrum shows that the oxygen atom content of the precursor M300 without ferric nitrate oxidation modification is 11.08 at, while the oxygen atom percentage of the precursors M300-FN21, M300-FN31 and M300-FN41 modified with different proportions of ferric nitrate oxidation modification is significantly increased, reaching 21.43 at%, 20.54 at% and 19.98 at%, respectively.

[0036] Example 4 Referring to Example 1, the difference is that the pre-oxidation temperature is 200°C, the resulting precursor is denoted as M200-FN31, and the resulting hard carbon material is denoted as M200-FN31-1400.

[0037] Example 5 Referring to Example 1, the difference is that the pre-oxidation temperature is 400°C, the resulting precursor is denoted as M400-FN31, and the resulting hard carbon material is denoted as M400-FN31-1400.

[0038] Example 6 Referring to Example 1, the difference is that the pre-calcination temperature is 200°C, the resulting precursor is denoted as M200-FN31(200), and the resulting hard carbon material is denoted as M200-FN31(200)-1400.

[0039] Example 7 Referring to Example 1, the difference is that the pre-calcination temperature is 400°C, the resulting precursor is denoted as M400-FN31(400), and the resulting hard carbon material is denoted as M400-FN31(400)-1400.

[0040] Example 8 Referring to Example 1, the difference is that the calcination temperature is 1200℃, the resulting precursor is denoted as M200-FN31, and the resulting hard carbon material is denoted as M200-FN31-1200.

[0041] Example 9 Referring to Example 1, the difference is that the pre-calcination temperature is 1300℃, the resulting precursor is denoted as M400-FN31, and the resulting hard carbon material is denoted as M400-FN31-1300.

[0042] Comparative Example 1 1g of coal tar pitch was pre-oxidized in a muffle furnace at 300℃ for 3h at a heating rate of 2℃ / min to obtain oxidized pitch (denoted as M-300). The oxidized asphalt was placed in a tube furnace for calcination (argon atmosphere, 1400℃, 2h, heating rate of 2℃ / min) to obtain hard carbon material (denoted as M300-1400). Figure 3 XRD patterns of M300-1400, M300-FN21-1400, M300-FN31-1400 and M300-FN41-1400 are shown in (a), (b), (c), (d), and (e) for the fitted peaks of the (002) diffraction peak of M300-1400. Figure 3 It can be seen that the (002) diffraction peaks of M300-FN31-1400 and M300-FN21-1400 are shifted towards smaller angles. Based on the calculation results of the Bragg equation, the interlayer spacing (d002) of samples M300-1400, M300-FN21-1400, M300-FN31-1400 and M300-FN51-1400 are 3.46 Å, 3.82 Å, 3.84 Å and 3.78 Å, respectively. The (002) diffraction peaks of M300-1400, M300-FN21-1400, M300-FN31-1400 and M300-FN41-1400 are fitted and analyzed: the (002) diffraction peaks are resolved into two crystal phases: pseudo-graphite phase and graphite phase. The pseudo-graphite phase peak area ratios of samples M300-1400, M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400 were 4.82%, 45.27%, 54.6%, and 38.11%, respectively. Figure 4 Raman fitting plots for M300-1400, M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400 are generated by... Figure 4 It can be seen that all samples are at 1350 cm. -1 and 1580 cm -1 It exhibits two characteristic peaks: 1350 cm⁻¹ -1 The D peak at that location corresponds to the sp peak caused by disorder and defects. 3 Vibration of hybrid structures, and 1580 cm -1 The G peak at that location originates from the sp generated by the graphite crystal phase. 2Hybridized bond stretching vibrations. The AD / AG value calculated by peak area integration can quantitatively characterize the graphitization degree of hard carbon materials. The AD / AG values ​​of samples M300-1400, M300-FN21-1400, M300-FN31-1400 and M300-FN41-1400 are 0.861, 1.866, 2.105 and 1.532, respectively. Among them, sample M300-FN31-1400 exhibits the highest degree of disorder; Figure 5 The N2 adsorption / desorption curves (a), pore size distribution (b), small angle X-ray extension (SAXS, c), and true density (d) of M300-1400 and M300-FN31-1400 are presented by [data missing]. Figure 5 It can be seen that both M300-1400 and M300-FN31-1400 exhibit Type I adsorption / desorption curves. Compared to M300-1400, M300-FN31-1400 shows a clearer hysteresis loop, indicating the presence of more micropores and mesopores. The specific surface areas of M300-1400 and M300-FN31-1400 are 1.68 and 10.80 m², respectively. 2 ·g -1 The closed-cell structure characteristics of M300-1400 and M300-FN31-1400 were investigated using true density testing and SAXS technology. Compared to hard carbon material M300-1400 prepared without ferric nitrate oxidized asphalt modification, hard carbon material M300-FN31-1400 prepared with ferric nitrate oxidized asphalt modification exhibited higher scattering vectors (Q = 0.1~0.5 Å). -1 The interval exhibits a distinct hump, a feature that confirms the presence of closed cells. Further true density testing results show that the closed-cell volumes of M300-1400 and M300-FN31-1400 are 0.037 cm³. 3 ·g -1 and 0.11cm 3 ·g -1 ; Figure 6 SEM images of M300-1400(a), M300-FN21-1400(b), M300-FN31-1400(c) and M300-FN41-1400(d) are provided by [the source]. Figure 6It is known that the hard carbon material M300-1400 prepared without ferric nitrate oxidative modification of pitch is prone to melting during the carbonization process, exhibiting a dense and smooth blocky morphology. However, the surface morphology of the hard carbon materials M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400 prepared with ferric nitrate oxidative modification of pitch changed significantly. This is mainly attributed to: the gas released from the decomposition of ferric nitrate during the pre-carbonization stage, forming a porous structure on the material surface; simultaneously, the generated Fe2O3 acts as a physical template, disrupting and regulating the original cross-linked structure, causing it to exhibit a granular accumulation. Figure 7 HRTEM plots for M300-1400(a), M300-FN21-1400(b), M300-FN31-1400(c), and M300-FN41-1400(d) are provided by... Figure 7 It can be seen that the hard carbon material M300-1400 prepared without ferric nitrate oxidized pitch exhibits a long-range ordered graphite-like microcrystalline structure. In contrast, the hard carbon materials M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400 prepared with ferric nitrate oxidized pitch show obvious closed pores and a more disordered microcrystalline structure. Notably, M300-FN31-1400 has the highest content of closed pores. Compared with the clear diffraction spots in the SAED analysis of M300-1400, M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400 exhibit diffuse diffraction rings, further confirming the increased disorder of the hard carbon materials. Furthermore, the carbon interlayer spacing of samples M300-1400, M300-FN21-1400, M300-FN31-1400 and M300-FN41-1400 are 0.348, 0.377, 0.381 and 0.368 nm, respectively, which is highly consistent with the interlayer spacing values ​​obtained from XRD analysis. The M300-1400, M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400 were used as electrode materials and assembled into a sodium-ion button cell (model CR2025) in an argon-filled glove box (O2 < 0.01 ppm, H2O < 0.01 ppm). The sodium-ion button cell consists of a sodium sheet, a separator, electrode sheets, and an electrolyte. The electrode sheets contain... The active materials are M300-1400, M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400; the electrolyte is a 1 mol / L NaClO4 solution (the solvent is EC and PC in a 1:1 volume ratio); the sodium-ion button battery was subjected to electrochemical performance testing under the following conditions: voltage range of 0.01~3.0V, current density of 30 mA·g. -1 The scan rate range is 0.2~2mV·s. -1 ; Figure 8 The first charge-discharge curve (a) and the contribution of ramp capacity and plateau capacity in the second discharge curve of sodium-ion button batteries assembled from M300-1400, M300-FN21-1400, M300-FN31-1400 and M300-FN41-1400 are shown in Figure (b). Figure 8 It can be seen that M300-1400, M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400 all exhibit typical hard carbon sodium storage characteristics: including plateau capacity below 0.1 V and slope capacity above 0.1 V. Because the hard carbon material M300-1400, prepared without ferric nitrate oxidized modified bitumen, has a relatively ordered bitumen-based hard carbon microcrystalline structure and a narrow interlayer spacing, it has a sodium storage capacity of only 84.6 mA·h·g. -1 The reversible charge capacity and first-cycle coulombic efficiency of the hard carbon materials M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400, prepared by ferric nitrate oxidized pitch modification, are 242.4 / 381.7 mA·h·g, respectively. -1 (63.5%), 292.0 / 385.9 mA·h·g -1 (75.6%), 225.8 / 307.2 mA·h·g -1 (73.5%); among them, sample M300-FN31-1400, due to its larger interlayer spacing and abundant closed-cell structure, had a plateau capacity contribution of 31.4 mA·h·g compared to sample M-300. -1 Increased to 207.86 mA·h·g -1It increased by 6 times compared to the hard carbon material M300-1400 prepared without ferric nitrate oxidative modification of pitch; Figure 9 The first charge-discharge curves of sodium-ion button batteries assembled from M200-FN31-1400, M300-FN31-1400, and M400-FN31-1400 are presented by [the following text is incomplete and likely refers to a separate document or data point]. Figure 9 It can be seen that the first-cycle reversible charge capacity / discharge reversible capacity (first-efficiency) of the sodium-ion button batteries assembled from M200-FN31-1400, M300-FN31-1400, and M400-FN31-1400 are 189.62 / 279.42 mA·h·g, respectively. -1 (67.86%), 292.0 / 385.9mA·h·g -1 (75.6%) and 160.41 / 252.89 mA·h·g -1 (63.43%); Figure 10 The first charge-discharge curves of sodium-ion button batteries assembled from M300-FN31(200)-1400, M300-FN31-1400, and M300-FN31(400)-1400 are presented. Figure 10 It can be seen that the first-cycle reversible charge capacity / discharge reversible capacity (first-cycle efficiency) of sodium-ion button batteries assembled from M300-FN31(200)-1400, M300-FN31-1400, and M300-FN31(400)-1400 are 213.16 / 295.51 mA·h·g, respectively. -1 (72.13%), 292.0 / 385.9mA·h·g -1 (75.6%) and 180.21 / 293.04 mA·h·g -1 (61.50%); Figure 11 The first charge-discharge curves of sodium-ion button batteries assembled from M300-FN31-1200, M300-FN31-1300, and M300-FN31-1400 are presented by [the following text is missing from the original] Figure 11 It can be seen that the first-cycle reversible charge capacity / discharge reversible capacity (first-efficiency) of sodium-ion button batteries assembled from M300-FN31-1200, M300-FN31-1300, and M300-FN31-1400 are 212.87 / 284.79 mA·h·g, respectively. -1 (74.75%), 219.12 / 301.88mA·h·g -1 (72.58%) and 292.0 / 385.9 mA·h·g -1 (75.6%); Figure 12Sodium-ion button cells assembled from M300-1400, M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400 achieve a voltage of 0.2 mV·s. -1 The CV curve at the scan rate is obtained from Figure 12 It can be seen that the first-cycle CV curves of M300-1400, M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400 show irreversible reduction peaks in the 0.4-1.0V range, which can be attributed to the formation of the SEI film. The redox peak intensity of M300-FN31-1400 is the strongest near 0.1V, and the CV results are in high agreement with the constant current charge-discharge curves. This indicates that the abundant closed pores and suitable interlayer spacing in the ferric nitrate-oxidized pitch-based hard carbon material help improve the reversible capacity of the material. Except for the first cycle, the CV curves of all electrodes have similar shapes and high overlap, indicating that the electrodes have good reversibility. Figure 13 Sodium-ion button cells assembled from M300-1400, M300-FN21-1400, M300-FN31-1400, and M300-FN41-1400 have an efficiency of 0.03~1 A·g. -1 Rate performance (a), impedance curves (b), and current density at different current densities (30 mA·g) -1 The cyclic stability curve (c) below is derived from... Figure 13 It can be seen that the unmodified hard carbon material M300-1400 at concentrations of 0.03, 0.05, 0.1, 0.2, 0.5 and 1 A·g -1 The reversible capacities at current densities are only 84.1, 78.1, 72.4, 65, 48.9, and 29.5 mA·h·g. -1 The hard carbon materials prepared by modifying pitch with different proportions of ferric nitrate all exhibited superior capacity compared to sample M300-1400, with sample M300-FN31-1400 demonstrating the best performance: at the same current density, its reversible capacity reached 293.3, 273.2, 245.7, 205.7, 140.4, and 79.2 mA·h·g. -1Its excellent rate performance is attributed to abundant closed pores and large interlayer spacing, which promotes the rapid transport of sodium ions. As can be seen from the electrochemical impedance spectroscopy (EIS) of M300-FN21-1400, M300-FN31-1400 and M300-FN41-1400, in the low frequency region, the spectrum shows a diagonal line feature, reflecting the sodium ion diffusion impedance (ZW); in the mid-to-high frequency region, a semi-circular arc appears, corresponding to the sodium ion charge transfer impedance (Rct). EIS test results show that, compared with the unmodified hard carbon material M300-1400 (Rct: 585.3 Ω), the hard carbon materials M300-FN21-1400 (Rct: 402.1 Ω), M300-FN31-1400 (Rct: 341.5 Ω), and M300-FN41-1400 (Rct: 434.8 Ω) prepared from asphalt with different proportions of ferric nitrate oxidized modification all exhibit reduced impedance values, with M300-FN31-1400 showing the lowest value. M300-FN31-1400 also demonstrates excellent cycling stability; at 0.03 A·g... -1 At the specified current density, the capacity retention rate is as high as 89.18% after 100 cycles, and it still has 260.4 mA·h·g after cycling. -1 Its reversible capacity far exceeds that of the M300-1400 (77.8 mA·h·g). -1 ); Figure 14 The CV curves (a) of a sodium-ion coin cell assembled from M300-FN31-140 at different scan rates, the relationship between log(i) and log(v), and the corresponding linear fit (b); Figure 14 It can be seen that even if the scan rate is increased to 2.0 mV·s -1 The CV curve of the sodium-ion button cell assembled from M300-FN31-140 still shows obvious redox peaks, indicating that the electrode has low polarization and high structural stability. According to the Ragone-Smith equation, the b-value is calculated based on the relationship between the redox peak current (i) and the scan rate (v) on the CV curve. Logi = alogv + logb; A b value close to 0.5 indicates that the electrode process is controlled by diffusion, while a b value close to 1 indicates that the process is dominated by capacitance. The linear fitting results show that the b value of the oxidation peak is 0.20959 and the b value of the reduction peak is 0.40362. Both values ​​are less than 0.5, which indicates that the electrochemical behavior of this electrode material during charging and discharging is mainly controlled by the diffusion process.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon material, characterized in that, Includes the following steps: Coal tar pitch is pre-oxidized to obtain oxidized pitch; The oxidized asphalt and an oxidizing metal compound are mixed to obtain a mixture; The mixture was subjected to pre-calcination and acid washing in sequence to obtain a precursor; The precursor is calcined to obtain the hard carbon material; The oxidizing metal compounds include oxidizing metal salts and / or oxidizing metal oxides.

2. The preparation method according to claim 1, characterized in that, The pre-oxidation temperature is 200~400℃, the time is 2~4h, and the heating rate to the pre-oxidation temperature is 1~3℃ / min.

3. The preparation method according to claim 1, characterized in that, The oxidizing metal salts include ferric nitrate and / or magnesium nitrate; The oxidizing metal oxides include copper oxide and / or cuprous oxide.

4. The preparation method according to claim 1 or 3, characterized in that, The mass ratio of the oxidized asphalt to the oxidizing metal compound is (2~4):

1.

5. The preparation method according to claim 1, characterized in that, The pre-calcination temperature is 200~400℃, the time is 0.5~2h, and the heating rate to the pre-calcination temperature is 1~3℃ / min.

6. The preparation method according to claim 1, characterized in that, The concentration of the acid solution used in the pickling process is 3~6 mol / L; The acid solution is a nitric acid solution and / or a hydrochloric acid solution.

7. The preparation method according to claim 1, characterized in that, The calcination temperature is 1200~1400℃, the time is 1~3h, and the heating rate to the calcination temperature is 1~3℃ / min.

8. The hard carbon material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the hard carbon material according to claim 8 in sodium-ion batteries.

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