A coal-based hard carbon anode material and its preparation method in sodium-ion batteries

Abstract

This invention relates to a coal-based hard carbon anode material, its preparation method, and a sodium-ion battery, comprising the following steps: pre-oxidizing coal at 190-410℃ for 1.5-6.5 h in an oxygen-containing atmosphere to obtain precursor 1; mixing precursor 1 with a pore-forming agent at a mass ratio of 1:0.2-4, and calcining at 600-900℃ for 1-5 h under an inert atmosphere or vacuum to obtain precursor 2; washing precursor 2 with water until neutral, and drying to obtain precursor 3; mixing precursor 3 with a coating material at a mass ratio of 1:0.01-0.15, and calcining at 1100-1600℃ for 0.5-5.5 h under an inert atmosphere or vacuum to obtain the coal-based hard carbon anode material. This invention solves the problem of high-value utilization of coal in sodium-ion battery anode materials, with low preparation cost and excellent performance.

Description

Technical Field

[0001] This invention relates to a coal-based hard carbon anode material and its preparation method, as well as a sodium-ion battery, belonging to the field of sodium-ion battery technology. Background Technology

[0002] Compared to scarce lithium resources, sodium resources are abundant and inexpensive. Therefore, sodium-ion batteries are considered the most likely replacement for lithium-ion batteries as the next generation of energy storage battery systems. Furthermore, sodium-ion batteries and lithium-ion batteries share very similar production processes, and lithium-ion batteries can provide sodium-ion batteries with experience in processes and technologies, making mass production of sodium-ion batteries imminent.

[0003] As a key material in sodium-ion batteries, the development of the anode material has lagged behind. Sodium ions have a large radius, making graphite anodes suitable for commercial lithium-ion batteries unsuitable for direct use due to their small interlayer spacing. Hard carbon materials, with their wider graphite interlayer spacing and abundant defects and pores, provide numerous sodium storage sites, making them suitable for preparing anode active materials for sodium-ion batteries.

[0004] Precursors for preparing hard carbon materials mainly include biomass, polymers, and coal. Currently, some biomass hard carbon has been commercially produced. However, biomass has a low fixed carbon content, resulting in high costs for preparing battery-grade hard carbon materials. Furthermore, the complexity and variability of biomass precursors make it difficult to ensure raw material consistency, which is a significant factor restricting the development of sodium-ion batteries. Coal is abundant, has a high carbon content, a high degree of aromaticity, and is inexpensive, making it considered a high-quality raw material for preparing hard carbon materials. However, materials obtained by directly carbonizing coal have a high degree of graphitization, small interlayer spacing, and poor sodium storage performance. Therefore, developing a low-cost preparation process for high-performance coal-based hard carbon anode materials is of great significance for the commercial application of sodium-ion batteries. Summary of the Invention

[0005] In view of the shortcomings of the prior art, one of the objectives of this invention is to provide a high-performance coal-based hard carbon anode material and its preparation method; another objective of this invention is to provide a sodium-ion battery.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] A method for preparing a coal-based hard carbon anode material includes the following steps:

[0008] S1. Coal is pre-oxidized at 185-410℃ for 1.5-6.5 h in an oxygen-containing atmosphere to obtain precursor 1;

[0009] S2. After mixing the precursor 1 and the pore-forming agent at a mass ratio of 1:0.2-4, calcine them at 600-900℃ for 1-5 hours under an inert atmosphere or vacuum to obtain the precursor 2.

[0010] The pore-forming agent is at least one of NaCl, ZnCl2, KCl, KOH, NaOH, Na2CO3, K2CO3, NaNO3, and KNO3.

[0011] S3. After washing the precursor 2 with water until it is neutral, dry it to obtain the precursor 3.

[0012] S4. After uniformly mixing the precursor 3 and the coating material at a mass ratio of 1:0.005-0.15, calcine them at 1100-1600℃ for 0.5-5.5h under an inert atmosphere or vacuum to obtain a coal-based hard carbon anode material.

[0013] The coating material is at least one of asphalt, phenolic resin, sucrose, and glucose. Preferably, the average particle size of the coating material is 15-74 μm, more preferably 25-60 μm. Preferably, the asphalt is high-temperature modified asphalt. Preferably, the softening point of the asphalt is 230-320℃, more preferably 250-300℃, and even more preferably 270-280℃.

[0014] Further, in S1, the coal is at least one of anthracite, sub-bituminous coal, and lignite. Preferably, the average particle size of the coal is 38-270 μm, more preferably 45-250 μm.

[0015] Further, in S1, a pre-oxidation treatment is performed at 200-400℃ for 2-6 hours, preferably at 220-380℃ for 2.5-5.5 hours.

[0016] More preferably, pre-oxidation treatment is carried out at 240-360℃ for 3-5 hours.

[0017] Furthermore, in S1, the oxygen-containing atmosphere is one of air, oxygen, or oxygen-enriched air atmosphere;

[0018] Preferably, the oxygen content in the oxygen-containing atmosphere is ≥20 vol%, more preferably 30-95 vol%.

[0019] Preferably, the pore-forming agent is a mixture of KCl and KOH, with a mass ratio of KCl to KOH of 0.5-1.5:0.5-1.5, more preferably 0.75-1.25:0.75-1.25.

[0020] Furthermore, in S2, the mass ratio of precursor 1 to pore-forming agent is 1:0.25-3.5, preferably 1:0.5-3, and more preferably 1:0.5-2;

[0021] Preferably, the material is calcined at 650-850℃ for 1.5-4.5 hours, and more preferably, at 700-800℃ for 2-4 hours.

[0022] Furthermore, in S4, the mass ratio of precursor 3 to coating material is 1:0.01-0.14, preferably 1:0.02-0.13;

[0023] Preferably, the sample is calcined at 1150-1550℃ for 1-5 hours; more preferably, it is calcined at 1200-1500℃ for 1.5-4.5 hours; and even more preferably, it is calcined at 1300-1400℃ for 2-4 hours.

[0024] Furthermore, in S2, the inert atmosphere is at least one of nitrogen or argon.

[0025] Furthermore, in S4, the inert atmosphere is at least one of nitrogen and argon.

[0026] A coal-based hard carbon anode material is prepared by the preparation method described above.

[0027] A sodium-ion battery includes a negative electrode sheet on which a coal-based hard carbon negative electrode material prepared by the preparation method described above is loaded.

[0028] Furthermore, coal-based hard carbon anode materials are used as active materials on the anode sheet.

[0029] The preparation method of this invention is simple and low-cost. First, oxygen atoms are introduced into the graphite layer of coal through pre-oxidation treatment, laying a foundation for subsequent high-temperature roasting. This effectively inhibits the high-temperature graphitization of coal during subsequent pore-forming and coating processes, resulting in a larger interlayer spacing of the final coal-based hard carbon anode material, overcoming the adverse effects of the high-temperature roasting process. At the same time, a closed-pore structure is formed by using pore-forming agents and coating materials, thereby providing a large number of sodium storage sites while also achieving a high first-cycle coulombic efficiency. This solves the problem of low capacity and first-cycle coulombic efficiency of existing coal-based hard carbon materials used as anode materials for sodium-ion batteries.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) The coal-based hard carbon anode material of the present invention is used in sodium-ion batteries and has excellent performance, with good performance in terms of reversible capacity, first-cycle coulombic efficiency and capacity retention.

[0032] (2) The pore-forming process in this invention can enrich the defects of the coal graphite layer and provide a large number of sodium storage pores, which greatly improves the sodium storage capacity; the coating process can reduce the specific surface area of ​​the hard carbon product, thereby improving the first-week coulombic efficiency.

[0033] (3) The main raw materials of the present invention are widely available and inexpensive. The processing technology adopted is simple to operate, highly controllable, and easy to achieve large-scale production, with a very broad prospect.

[0034] (4) This invention can solve the problem of high-value utilization of coal in sodium-ion battery anode materials, and has low preparation cost and excellent performance. Attached Figure Description

[0035] Figure 1 This is a process flow diagram for preparing the coal-based hard carbon anode material of the present invention.

[0036] Figure 2 A comparison of X-ray diffraction patterns of anthracite as raw material, the coal-based hard carbon material of Example 1, and the coal-based hard carbon material of Comparative Example 1.

[0037] Figure 3 This is a comparison diagram of the pore size distribution of the precursor 3 in Examples 1, 4, 5 and 6.

[0038] Figure 4 This is a comparison of the specific surface area analysis of coal-based hard carbon materials in Examples 1, 7, 8, and 9.

[0039] Figure 5 The image shows a SEM image of the coal-based hard carbon anode material prepared in Example 1. Detailed Implementation

[0040] The present invention will be described in detail below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. Unless otherwise specified, the relevant percentages refer to mass percentages.

[0041] Example 1

[0042] This embodiment provides a method for preparing a coal-based hard carbon anode material, including the following steps:

[0043] S1: The anthracite is crushed and screened to obtain powder with an average particle size of 74μm; the above material is placed in a muffle furnace and heated to 300℃ in air at 3℃ / min and held for 4h for pre-oxidation, and then cooled naturally to obtain precursor 1;

[0044] S2: Mix the pre-oxidized precursor 1 with KOH (pore-forming agent) at a mass ratio of 1:0.5 to obtain precursor 2;

[0045] S3: Precursor 2 is placed in an atmosphere furnace and calcined under an argon atmosphere. The temperature is increased to 700℃ at 5℃ / min and held for 2 hours. After natural cooling, precursor 3 is obtained.

[0046] S4: After washing precursor 3 with water until neutral, dry it and then mix it thoroughly with high-temperature modified asphalt (softening point of 270-280℃) with an average particle size of 38μm at a mass ratio of 1:0.05 to obtain precursor 4;

[0047] S5: Precursor 4 is placed in an atmosphere furnace and calcined under an argon atmosphere. The temperature is increased to 1100℃ at 5℃ / min and then increased to 1400℃ at 3℃ / min, and held for 2 hours to obtain anthracite-based hard carbon anode material.

[0048] The prepared anthracite-based hard carbon anode material, conductive carbon black, and polyvinylidene fluoride were slurried in a mass ratio of 8:1:1 and coated onto a copper foil current collector. The mixture was then dried in a vacuum drying oven at 80°C for 12 hours to obtain a carbon anode. Using the carbon anode as the working electrode, a sodium metal sheet as the anode, glass fiber as the separator, and 1 mol / L NaClO4-EC:DEC = 1:1 Vol% as the electrolyte, CR2032 coin cells were assembled in an argon-filled dry glove box. Electrochemical performance tests were conducted in a 25°C constant temperature oven, with a voltage range of 0.01–3.00 V.

[0049] Example 2

[0050] Repeat Example 1, except that in S1, sub-bituminous coal is used instead of anthracite.

[0051] Example 3

[0052] Repeat Example 1, except that in S1, lignite is used instead of anthracite.

[0053] Example 4

[0054] Repeat Example 1, except that the pore-forming agent in S2 is a mixture of KOH and Na2CO3 in a 1:1 mass ratio.

[0055] Example 5

[0056] Repeat Example 1, except that the pore-forming agent in S2 is a mixture of NaOH and Na2CO3 in a 1:1 mass ratio.

[0057] Example 6

[0058] Repeat Example 1, except that the pore-forming agent in S2 is a mixture of KOH and KCl in a 1:1 mass ratio.

[0059] Example 7

[0060] Repeat Example 1, except that the coating material in S4 is sucrose.

[0061] Example 8

[0062] Example 1 was repeated, except that the coating material in S4 was phenolic resin (from Aladdin Reagent Company).

[0063] Example 9

[0064] Repeat Example 1, except that the coating material in S4 is glucose.

[0065] Example 10

[0066] Repeat Example 1, except that the heat preservation temperature in S1 is 400°C.

[0067] Example 11

[0068] Repeat Example 1, except that the heat preservation temperature in S1 is 200°C.

[0069] Example 12

[0070] Repeat Example 1, except that the heat preservation time in S1 is 2 hours.

[0071] Example 13

[0072] Repeat Example 1, except that the heat preservation time in S1 is 6 hours.

[0073] Example 14

[0074] Example 1 is repeated, except that the mass ratio of precursor 1 to pore-forming agent in S2 is 1:4.

[0075] Example 15

[0076] Example 1 is repeated, except that the mass ratio of precursor 1 to pore-forming agent in S2 is 1:1.

[0077] Example 16

[0078] Example 1 is repeated, except that the mass ratio of precursor 1 to pore-forming agent in S2 is 1:0.25.

[0079] Example 17

[0080] Repeat Example 1, except that the heat preservation temperature in S3 is 600°C.

[0081] Example 18

[0082] Repeat Example 1, except that the heat preservation temperature in S3 is 900°C.

[0083] Example 19

[0084] Example 1 is repeated, except that the mass ratio of precursor 3 to coating material in S4 is 1:0.01.

[0085] Example 20

[0086] Example 1 is repeated, except that the mass ratio of precursor 3 to coating material in S4 is 1:0.1.

[0087] Example 21

[0088] Example 1 is repeated, except that the mass ratio of precursor 3 to coating material in S4 is 1:0.15.

[0089] Example 22

[0090] Repeat Example 1, except that the heat preservation temperature in S5 is 1100°C.

[0091] Example 23

[0092] Repeat Example 1, except that the heat preservation temperature in S5 is 1200°C.

[0093] Example 24

[0094] Repeat Example 1, except that the heat preservation temperature in S5 is 1600℃.

[0095] Example 25

[0096] Repeat Example 1, except that the heat preservation time in S5 is 1 hour.

[0097] Example 26

[0098] Repeat Example 1, except that the heat preservation time in S5 is 4 hours.

[0099] Example 27

[0100] Repeat Example 1, except that the heat preservation time in S5 is 4.5h.

[0101] Example 28

[0102] Repeat Example 1, except that the heat preservation temperature in S1 is 410°C.

[0103] Example 29

[0104] Repeat Example 1, except that the heat preservation temperature in S1 is 190°C.

[0105] Example 30

[0106] Repeat Example 1, except that the heat preservation time in S1 is 1.5h.

[0107] Example 31

[0108] Repeat Example 1, except that the heat preservation time in S1 is 6.5h.

[0109] Example 32

[0110] Example 1 is repeated, except that the mass ratio of precursor 1 to pore-forming agent in S2 is 1:0.2.

[0111] Example 33

[0112] Example 1 is repeated, except that the mass ratio of precursor 3 to coating material in S4 is 1:0.005.

[0113] Example 34

[0114] Repeat Example 1, except that the heat preservation time in S5 is 0.5h.

[0115] Example 35

[0116] Repeat Example 1, except that the heat preservation time in S5 is 5.5h.

[0117] Comparative Example 1

[0118] Repeat Example 1, except that the pre-oxidation treatment step in S1 is omitted.

[0119] Comparative Example 2

[0120] Example 1 is repeated, except that the mass ratio of precursor 1 to pore-forming agent in S2 is 1:4.5.

[0121] Comparative Example 3

[0122] Repeat Example 1, except that the heat preservation temperature in S3 is 550°C.

[0123] Comparative Example 4

[0124] Repeat Example 1, except that the heat preservation temperature in S3 is 950°C.

[0125] Comparative Example 5

[0126] Example 1 is repeated, except that the mass ratio of precursor 3 to coating material in S4 is 1:0.16.

[0127] Comparative Example 6

[0128] Repeat Example 1, except that the heat preservation temperature in S5 is 1050°C.

[0129] Comparative Example 7

[0130] Example 1 is repeated, except that the heat preservation temperature in S5 is 1650°C.

[0131] The relevant performance test results of the embodiments are shown in Table 1:

[0132] Table 1

[0133]

[0134]

[0135] Note: The current density for reversible capacity testing is 0.01 A / g, and the current density for cyclic testing is 0.5 A / g.

[0136] As can be seen from the data in Table 1, the coal-based hard carbon materials prepared by this invention all exhibit good performance. Considering reversible capacity, first-cycle coulombic efficiency, and capacity retention, the coal-based hard carbon material of Example 6 demonstrates the most outstanding performance, exhibiting excellent properties in all aspects. Furthermore, its coating material is high-temperature modified pitch, resulting in lower preparation costs. Additionally, the coal-based hard carbon materials prepared in Examples 1, 10, 13, 18, 26, and 27 all possess good reversible capacity, first-cycle coulombic efficiency, and capacity retention.

[0137] Example 2, which simply changed the raw material to bituminous coal, showed a higher reversible capacity. This may be because bituminous coal has a lower degree of graphitization and a larger interlayer spacing, resulting in a higher reversible capacity. However, due to its higher ash content, the first-week coulombic efficiency and capacity retention rate are lower.

[0138] Example 3, which simply changed the raw material to lignite, ultimately showed a higher reversible capacity. The possible reason is that lignite has a lower degree of graphitization and a larger interlayer spacing, so the material has a higher reversible capacity. However, due to its higher ash content, the first-week coulombic efficiency and capacity retention rate are lower.

[0139] In Example 4, simply changing the pore-forming agent in S2 to KOH:Na2CO3 = 1:1 resulted in a decrease in reversible capacity, first-cycle coulombic efficiency, and capacity retention, indicating a deterioration in pore-forming effect.

[0140] In Example 5, simply changing the pore-forming agent in S2 to NaOH:NaCO3 = 1:1 resulted in a decrease in reversible capacity, first-cycle coulombic efficiency, and capacity retention, indicating a deterioration in pore-forming effect.

[0141] In Example 6, simply changing the pore-forming agent in S2 to KOH:KCl = 1:1, the reversible capacity, first-cycle coulombic efficiency, and capacity retention were all improved, indicating a better pore-forming effect.

[0142] Example 7 changed the coating material in S4 to sucrose, which improved the reversible capacity, but reduced the first-week coulombic efficiency and capacity retention.

[0143] Example 8 changed the coating material in S4 to phenolic resin, which improved the reversible capacity, but reduced the first-week coulombic efficiency and capacity retention.

[0144] Example 9 changed the coating material in S4 to glucose, which improved the reversible capacity, but reduced the first-week coulombic efficiency and capacity retention.

[0145] The coal-based hard carbon material prepared in Example 10 only increased the holding temperature in step S1, but the difference in the performance of the prepared material was not significant. This indicates that the pre-oxidation degree in Example 1 has reached or is close to the limit, and further increasing the pre-oxidation temperature does not significantly improve the final performance of the obtained material.

[0146] The coal-based hard carbon material prepared in Example 11 only reduced the holding temperature in step S1, resulting in a decrease in the pre-oxidation degree of precursor 1 and a decrease in the reversible capacity of the prepared material.

[0147] The coal-based hard carbon material prepared in Example 12 only reduced the holding time in step S1, resulting in a decrease in the pre-oxidation degree of precursor 1 and a decrease in the reversible capacity of the prepared material.

[0148] The coal-based hard carbon material prepared in Example 13 only increased the holding time in step S1, but the performance difference of the prepared material was not significant, indicating that the pre-oxidation degree of Example 1 had reached or approached the limit.

[0149] The coal-based hard carbon material prepared in Example 14 only increased the amount of pore-forming agent added in step S2, but the reversible capacity of the prepared material decreased, indicating that excessive pore formation is not conducive to performance improvement.

[0150] The coal-based hard carbon material prepared in Example 15 only increased the amount of pore-forming agent added in step S2, but the reversible capacity of the prepared material decreased, indicating that excessive pore formation is not conducive to performance improvement.

[0151] The coal-based hard carbon material prepared in Example 16 only reduced the amount of pore-forming agent added in step S2, but the reversible capacity of the prepared material was reduced, indicating that the pores were fewer and the sodium storage performance was poor.

[0152] The coal-based hard carbon material prepared in Example 17 only reduced the holding temperature in step S3, but the reversible capacity of the prepared material decreased. The possible reason is that the lower temperature is not conducive to pore formation, resulting in poor performance.

[0153] The coal-based hard carbon material prepared in Example 18 only increased the heat preservation temperature in step S3, but the reversible capacity of the prepared material decreased, indicating that excessively high temperature is not conducive to pore formation and leads to poor performance.

[0154] The coal-based hard carbon material prepared in Example 19 only reduced the amount of coating material added in step S4, but the coulombic efficiency of the prepared material decreased in the first week. The possible reason is that the coating material was insufficient and the material had a larger specific surface area.

[0155] The coal-based hard carbon material prepared in Example 20 only increased the amount of coating material added in step S4, but the reversible capacity of the prepared material decreased. The possible reason is that too much coating material will hinder the inward transport of sodium ions.

[0156] The coal-based hard carbon material prepared in Example 21 only significantly increased the amount of coating material added in step S4, but the reversible capacity of the prepared material was greatly reduced. The possible reason is that too much coating material will hinder the inward transport of sodium ions.

[0157] The coal-based hard carbon material prepared in Example 22 only significantly reduced the holding temperature in step S5, but the reversible capacity of the prepared material was greatly reduced, indicating that the lower temperature is not conducive to the formation of sodium storage structure.

[0158] The coal-based hard carbon material prepared in Example 23 only reduced the holding temperature in step S5, but the reversible capacity of the prepared material decreased, indicating that the lower temperature is not conducive to the formation of sodium storage structure.

[0159] The coal-based hard carbon material prepared in Example 24 only increased the holding temperature in step S5, but the reversible capacity of the prepared material decreased, indicating that the higher temperature and the higher degree of graphitization were not conducive to the intercalation of sodium ions.

[0160] The coal-based hard carbon material prepared in Example 25 only reduced the holding time in step S5, but the reversible capacity of the prepared material was reduced, indicating that the carbonization process was not completed, which is not conducive to the formation of sodium storage structure.

[0161] The coal-based hard carbon material prepared in Example 26 only increased the holding time in step S5, but the difference in the internal structure of the prepared material was not significant. The possible reason is that the carbonization process was already completed under the holding time conditions of Example 1.

[0162] The coal-based hard carbon material prepared in Example 27 only increased the holding time in step S5, but the difference in the internal structure of the prepared material was not significant.

[0163] Example 28 only increased the heat preservation temperature in S1, and the properties of the prepared material decreased slightly, indicating that the degree of pre-oxidation was slightly reduced.

[0164] Example 29 only reduced the holding temperature in S1, and the reversible capacity of the prepared material decreased, indicating that the degree of pre-oxidation was reduced.

[0165] Example 30 only reduced the holding time in S1, and the reversible capacity of the prepared material decreased, indicating that the degree of pre-oxidation was reduced.

[0166] Example 31 only increased the heat preservation time in S1, and the difference in the performance of the prepared materials was not significant, indicating that the degree of pre-oxidation had reached its maximum.

[0167] Example 32 only reduced the amount of pore-forming agent added in S2, but the reversible capacity of the prepared material decreased, indicating that less pore formation is not conducive to the formation of sodium storage structure. The amount of pore-forming agent added needs to be controlled within an appropriate range to obtain excellent performance.

[0168] Example 33 only reduced the amount of coating material added in S4, but the first-week coulombic efficiency of the prepared material decreased. The possible reason is that the amount of coating material added was reduced, and the specific surface area of ​​the final material increased.

[0169] Example 34 only reduced the holding time in step S5, but the reversible capacity of the prepared material was reduced. The possible reason is that the lower temperature is not conducive to the formation of sodium storage structure.

[0170] Example 35 only increased the holding time in step S5, but the difference in the inward direction of the prepared material was not significant. The possible reason is that the carbonization process was already completed under the conditions of Example 1.

[0171] The test results for the comparative examples are shown in Table 2:

[0172] Table 2

[0173]

[0174] Note: The current density for reversible capacity testing is 0.01 A / g, and the current density for cyclic testing is 0.5 A / g.

[0175] Comparative Example 1 omitted only the pre-oxidation treatment step in S1, but the properties of the prepared material were significantly reduced. This resulted in a lack of oxygen atom inhibition during the subsequent high-temperature calcination process, leading to a smaller interlayer spacing of graphite. Figure 2 As shown, this is not conducive to the transport and storage of sodium ions.

[0176] Comparative Example 2 only increased the amount of pore-forming agent added in S2, but the reversible capacity of the prepared material decreased, indicating that excessive pore formation is not conducive to performance improvement.

[0177] Comparative Example 3 only reduced the insulation temperature in S3, but the reversible capacity of the prepared material decreased, indicating that lower temperature is not conducive to pore formation, resulting in poor performance.

[0178] Comparative Example 4 only increased the insulation temperature in S3, but the reversible capacity of the prepared material decreased, indicating that higher temperatures are not conducive to pore formation, resulting in poor performance.

[0179] Comparative Example 5 only increased the amount of coating material added in S4, but the reversible capacity of the prepared material decreased. The possible reason is that too much coating material resulted in an excessively thick coating layer, which hindered the inward transport of sodium ions.

[0180] Comparative Example 6 only reduced the heat preservation temperature in S5, but the properties of the prepared material were significantly reduced in all aspects. The possible reason is that the lower temperature is not conducive to the formation of sodium storage structure.

[0181] Comparative Example 7 only increased the holding temperature in S5, but the reversible capacity of the prepared material decreased. The possible reason is that the higher temperature resulted in a higher degree of graphitization, which is not conducive to the intercalation of sodium ions.

[0182] analyze Figure 2 It can be observed that the 2θ of the (002) peak of the raw anthracite is similar to that of the coal-based hard carbon material prepared in Example 1, indicating that the interlayer spacing of graphite is similar and the pre-oxidation step can inhibit the high-temperature graphitization process. However, due to the lack of a pre-oxidation process, the 2θ of the (002) peak of the coal-based hard carbon material prepared in Comparative Example 1 is larger than that of the raw material, the interlayer spacing of graphite is smaller, the degree of graphitization is higher, which is not conducive to the transport and storage of sodium ions.

[0183] analyze Figure 3 It can be observed that Example 6 has the best pore-forming effect, with most pores being micropores (<2nm). Example 1 has a slightly worse pore-forming effect, with a lower number of micropores. This may be because KCl can synergistically work with KOH to promote pore formation. In contrast, Examples 4 and 5 have poorer pore-forming effects, with most pores being mesopores (>2nm), which are not conducive to the storage of sodium ions.

[0184] analyze Figure 4 It can be observed that the hard carbon materials obtained in Examples 1, 8, 9 and 7 are ranked from smallest to largest by specific surface area. This indicates that the coating effect of high-temperature modified asphalt is the best, followed by phenolic resin and glucose, and sucrose is the worst.

[0185] In summary, the method of this invention can yield a coal-based hard carbon anode material for sodium-ion batteries with excellent comprehensive performance, providing a new path for the high-value utilization of coal.

[0186] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. A method for preparing a coal-based hard carbon anode material, characterized in that, Includes the following steps: S1. Coal is pre-oxidized at 300-410℃ for 2-6.5 hours under an oxygen-containing atmosphere to obtain precursor 1; The coal in question is anthracite; S2. After mixing the precursor 1 and the pore-forming agent at a mass ratio of 1:0.25-0.5, calcine them at 650-850℃ for 1-5 hours under an inert atmosphere or vacuum to obtain the precursor 2. The pore-forming agent is composed of KCl and KOH mixed in a 1:1 mass ratio; S3. After washing the precursor 2 with water until it is neutral, dry it to obtain the precursor 3. S4. After uniformly mixing the precursor 3 and the coating material at a mass ratio of 1:0.01-0.05, calcine them at 1400-1500℃ for 1.5-5.5h under an inert atmosphere or vacuum to obtain a coal-based hard carbon anode material. The coating material is asphalt, which is high-temperature modified asphalt, and the softening point of the asphalt is 230-320℃.

2. The preparation method according to claim 1, characterized in that, In S1, the average particle size of the coal is 38-270 μm.

3. The preparation method according to claim 2, characterized in that, In S1, the average particle size of the coal is 45-250 μm.

4. The preparation method according to claim 1, characterized in that, In S1, pre-oxidation is carried out at 300-400℃ for 2-6 hours.

5. The preparation method according to claim 4, characterized in that, In S1, pre-oxidation treatment is carried out at 300-380℃ for 2.5-5.5 hours.

6. The preparation method according to claim 4, characterized in that, In S1, pre-oxidation is carried out at 300-360℃ for 3-5 hours.

7. The preparation method according to claim 1, characterized in that, In S1, the oxygen-containing atmosphere is one of air, oxygen, or oxygen-enriched air atmosphere; the oxygen content in the oxygen-containing atmosphere is ≥20 vol.

8. The preparation method according to claim 7, characterized in that, In S1, the oxygen content in the oxygen-containing atmosphere is 30-95 vol.

9. The preparation method according to claim 1, characterized in that, In S2, calcination is carried out at 650-850℃ for 1.5-4.5 hours.

10. The preparation method according to claim 1, characterized in that, In S2, calcination is carried out at 700-800℃ for 2-4 hours.

11. The preparation method according to claim 1, characterized in that, In S4, calcination is carried out at 1400-1500℃ for 1.5-5 hours.

12. The preparation method according to claim 11, characterized in that, In S4, calcination is carried out at 1400-1500℃ for 1.5-4.5 hours.

13. The preparation method according to claim 12, characterized in that, In S4, calcination is carried out at 1400℃ for 2-4 hours.

14. The preparation method according to claim 1, characterized in that, In S4, the average particle size of the coating material is 15-74 μm.

15. The preparation method according to claim 14, characterized in that, In S4, the average particle size of the coating material is 25-60 μm.

16. The preparation method according to claim 1, characterized in that, In S2, the inert atmosphere is at least one of nitrogen or argon.

17. The preparation method according to claim 1, characterized in that, In S4, the inert atmosphere is at least one of nitrogen and argon.

18. A coal-based hard carbon anode material, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

19. A sodium-ion battery, comprising a negative electrode, characterized in that, The negative electrode sheet is loaded with a coal-based hard carbon negative electrode material prepared by any one of claims 1-7.

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