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

Abstract

The invention belongs to the technical field of sodium ion batteries, and particularly relates to a phenolic resin-based hard carbon material as well as a preparation method and application thereof. Compared with the prior art, the method provided by the invention has the characteristic of simple and convenient process, the structural design is directly carried out based on the hard carbon material body, and a complicated coating or deposition process is not needed; the closed pore volume of hard carbon and the interlayer spacing and thickness of carbon layers can be accurately regulated and controlled by changing the addition amount of phosphoric acid and the temperature and time of high-temperature heat treatment; besides, the obtained hard carbon material has a rich closed-pore structure, can be used as a sodium-ion battery negative electrode material, and shows excellent first coulombic efficiency, high platform capacity and high reversible specific capacity, so that the electrochemical performance of a sodium-ion battery is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and particularly relates to a phenolic resin-based hard carbon material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries have emerged as a promising alternative to lithium-ion batteries due to the abundant natural reserves of sodium and their cost-effectiveness. However, developing high-performance, low-cost anode materials remains a key challenge for their commercial application. Among various candidate materials, including graphite and alloy compounds, hard carbon stands out as the most viable anode choice due to its economic advantages, superior theoretical specific capacity (typically exceeding 300 mAh / g), and unique low-potential plateau for sodium storage.

[0003] Due to their inherent structural characteristics (including disordered nanodomain orientation, large interlayer spacing (typically 0.38–0.42 nm), and chaotic layered topology), hard carbon materials exhibit a distinct dual-region behavior in their charge-discharge curves: a high-potential slope region (relative to Na⁺ / Na > 0.1 V) shows charge storage dominated by pseudocapacitance, and experimental evidence suggests that its capacity is related to chemisorption at edge sites and redox reactions of surface functional groups; the low-potential plateau region (<0.1 V) originates from multi-stage sodium intercalation and the filling of quasi-metallic sodium clusters within sub-nanometer closed pores (0.5–1.2 nm). Improving the capacity of the plateau region is beneficial for the commercial application of high-energy-density sodium-ion batteries. Therefore, precisely controlling the molecular structure of carbon precursors to passivate surface defects and enrich the internal closed-pore structure of hard carbon materials has become a key strategy for improving reversible capacity.

[0004] Studies have shown that the reversible capacity of sodium-ion batteries mainly originates from the plateau capacity. The sodium storage mechanism in the plateau region is primarily related to the characteristics of nanopores or closed pores. Therefore, increasing the number of closed pores in hard carbon is crucial. However, current closed-pore construction technologies, such as soft carbon-hard carbon composites and pore-forming agents, typically face the dual challenges of complex processes and exponentially increasing costs. For example, Sun et al. published an article entitled "Rationally Regulating Closed Pore Structures by Pitch Coating to Boost Sodium Storage Performance of Hard Carbon in Low-voltage Platforms" in *Advanced Functional Materials* (2024, 2403642), which precisely prepared a rich closed-pore structure with a suitable closed-pore size of 0.45 nm by chemically crosslinking pre-oxidized phenolic resin with a small amount of pitch during carbonization. Zhou et al., in their article "Tailored Regulation of Graphite Microcrystals via TandemCatalytic Carbonization for Enhanced Electrochemical Performance of Hard Carbon in the Low-Voltage Plateau" published in *Advanced Functional Materials* (2024, 2416061), used zinc chloride as a catalyst to precisely control the micro / nano structure, achieving an improvement in the capacity of hard carbon in the low-voltage plateau region. In addition, some studies have used a simple mixture of cured epoxy resin and phosphoric acid (such as Chinese patent publication number CN119683606A), followed by water washing to remove the phosphoric acid, and then high-temperature carbonization to obtain hard carbon materials. Although the addition of phosphoric acid is intended to eliminate surface defects, simply mixing epoxy resin carbon with phosphoric acid cannot effectively generate chemical bonds that can alter the molecular structure. This results in limited reversible capacity and plateau capacity, making it difficult to meet commercial needs. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a phenolic resin-based hard carbon material, its preparation method and application, wherein the phenolic resin-based hard carbon material obtained by the preparation method has a high sodium storage platform capacity.

[0006] This invention provides a method for preparing phenolic resin-based hard carbon material, comprising the following steps:

[0007] S1) The phenolic resin is heated in a protective atmosphere to undergo a first carbonization treatment to obtain the carbonized product;

[0008] S2) The carbonized product is mixed with phosphoric acid and subjected to a second carbonization treatment in a protective atmosphere to obtain a cross-linked carbonized product;

[0009] S3) The cross-linked carbonization product is purified to remove phosphate and obtain purified cross-linked carbonization product;

[0010] S4) The purified cross-linked carbonization product is subjected to high-temperature treatment in a protective atmosphere to obtain phenolic resin-based hard carbon material.

[0011] Preferably, the heating rate in step S1) is 5~15℃ / min;

[0012] The temperature of the first carbonization treatment is 500℃~900℃; the time of the first carbonization treatment is 1~3h.

[0013] Preferably, the mass concentration of the phosphoric acid is 80% to 85%;

[0014] The mass of the phosphoric acid is 10% to 90% of the mass of the carbonization product.

[0015] Preferably, in step S2), the carbonized product is mixed with phosphoric acid in an aqueous ethanol solution, dried, and then subjected to a second carbonization treatment.

[0016] Preferably, the second carbonization treatment is carried out at 400℃~600℃; the second carbonization treatment time is 1~4h.

[0017] Preferably, the purification process in step S3) specifically involves washing with water and drying.

[0018] Preferably, the high-temperature treatment in step S4) is at a temperature of 1300℃~1500℃; and the high-temperature treatment time is 1~5 h.

[0019] The present invention also provides a phenolic resin-based hard carbon material prepared by the above preparation method.

[0020] Preferably, the carbon interlayer spacing of the phenolic resin-based hard carbon material is 0.37~0.40 nm.

[0021] The present invention also provides a sodium-ion battery, including a negative electrode; the negative electrode includes a phenolic resin-based hard carbon material prepared by the above preparation method.

[0022] Compared with the prior art, the preparation method provided by the present invention has the following advantages:

[0023] 1) The method of the present invention has the characteristics of simple process, and the structural design is carried out directly based on the hard carbon material body, without the need for complicated coating or deposition process;

[0024] 2) In the technical solution of the present invention, the closed-cell volume of hard carbon, the interlayer spacing and thickness of carbon layers can be precisely controlled by changing the amount of phosphoric acid added and the high-temperature heat treatment temperature and time;

[0025] 3) The hard carbon material prepared by this invention has abundant closed-pore structure and can be used as a negative electrode material for sodium-ion batteries. It exhibits excellent first coulombic efficiency, high plateau capacity and high reversible specific capacity, thereby significantly improving the electrochemical performance of sodium-ion batteries. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope image of the phenolic hard carbon material obtained in Example 5 of the present invention;

[0027] Figure 2 This is a high-resolution transmission electron microscope image of the phenolic hard carbon material obtained in Example 5 of the present invention;

[0028] Figure 3 The infrared spectrum of the phenolic hard carbon material obtained in Example 5 of this invention;

[0029] Figure 4 The image shows a comparison of the first charge-discharge cycles of sodium-ion batteries using phenolic hard carbon materials obtained in Examples 1-6 of this invention and Comparative Example 1 as negative electrodes.

[0030] Figure 5 The graph shows a comparison of the ramp capacity and plateau capacity of sodium-ion batteries using phenolic hard carbon materials obtained in Examples 1-6 of this invention as negative electrodes and Comparative Example 1. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention provides a method for preparing a phenolic resin-based hard carbon material, comprising the following steps: S1) heating phenolic resin in a protective atmosphere to perform a first carbonization treatment to obtain a carbonized product; S2) mixing the carbonized product with phosphoric acid and performing a second carbonization treatment in a protective atmosphere to obtain a cross-linked carbonized product; S3) purifying the cross-linked carbonized product to remove phosphates, obtaining a purified cross-linked carbonized product; S4) subjecting the purified cross-linked carbonized product to high-temperature treatment in a protective atmosphere to obtain a phenolic resin-based hard carbon material.

[0033] This invention regulates the molecular structure by controlling the degree of secondary crosslinking, thereby generating new chemical bonds such as COP, CP-O3, and C2-P-O2, achieving closed-pore regulation and effective enrichment of hard carbon materials. At the same time, it significantly improves the electrochemical performance of hard carbon as a negative electrode material for sodium-ion batteries, including initial coulombic efficiency, reversible capacity, and plateau capacity, providing a technical route for the design and preparation of hard carbon negative electrode materials for sodium-ion batteries.

[0034] In this invention, there are no special restrictions on the source of any raw materials; they can be commercially available.

[0035] In a specific embodiment of the present invention, the phenolic resin is preferably a phenolic resin prepared from resorcinol and formaldehyde; the degree of crosslinking of the phenolic resin is preferably 70% to 90%; optionally, the degree of crosslinking of the phenolic resin is 70%, 75%, 80%, 81%, 82%, 83%, 84%, 85%, 85%, 87%, 88%, 89%, 90% or any two of the above values.

[0036] The phenolic resin is heated in a protective atmosphere for a first carbonization treatment to obtain a carbonized product. The protective atmosphere can be any atmosphere known to those skilled in the art and is not particularly limited; in this invention, argon and / or nitrogen are preferred. The heating rate is preferably 5~15℃ / min; optionally, the heating rate is 5℃ / min, 8℃ / min, 10℃ / min, 12℃ / min, 15℃ / min, or any range between two of the above values. The temperature of the first carbonization treatment is preferably 500℃~900℃; optionally, the temperature of the first carbonization treatment is 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, or any range between two of the above values. The time of the first carbonization treatment is preferably 1~3 h; optionally, the time of the first carbonization treatment is 1 h, 1.5 h, 2 h, 2.5 h, 3 h, or any range between two of the above values.

[0037] The carbonization product is mixed with phosphoric acid; the mass concentration of the phosphoric acid is preferably 80%~85%; the mass of the phosphoric acid is preferably 10%~90% of the mass of the carbonization product; optionally, the mass of the phosphoric acid is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% of the mass of the carbonization product or any two of the above values; the present invention precisely controls the degree of crosslinking of phenolic resin carbon by adjusting the amount of phosphoric acid added, thereby enriching the closed-pore structure inside the phenolic resin-based hard carbon, and significantly improving the electrochemical performance of phenolic resin-based hard carbon as a negative electrode material for sodium-ion batteries, including initial coulombic efficiency, reversible capacity and plateau capacity.

[0038] In a specific embodiment of the present invention, the carbonized product is mixed with phosphoric acid in an ethanol-water solution, dried, and then subjected to a second carbonization treatment under a protective atmosphere to obtain a cross-linked carbonized product; the volume ratio of ethanol to water in the ethanol-water solution is preferably 1:(0.5~1.5), more preferably 1:(0.8~1.2), and even more preferably 1:1; the drying method is preferably vacuum drying; the drying temperature is preferably 100℃~150℃, more preferably 110℃~130℃, and even more preferably 120℃; the drying time is preferably 5~15 h, more preferably 8~12 h, and even more preferably 10 h.

[0039] In one specific embodiment of the present invention, the temperature of the second carbonization treatment is preferably 400℃~600℃; optionally, the temperature of the second carbonization treatment is 400℃, 450℃, 500℃, 550℃, 600℃ or any two of the above values; the time of the second carbonization treatment is preferably 1~4 h; optionally, the time of the second carbonization treatment is 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h or any two of the above values.

[0040] The cross-linked carbonization product is purified to remove phosphate, resulting in a purified cross-linked carbonization product. The purification process specifically involves washing with water and drying. More specifically, the product is washed with deionized water until neutral and then dried. The drying temperature is preferably 60℃~100℃, more preferably 70℃~90℃, and even more preferably 80℃. The drying time is preferably 1~5 h, more preferably 2~4 h, and even more preferably 2~3 h.

[0041] The purified cross-linked carbonization product is subjected to high-temperature treatment in a protective atmosphere to obtain phenolic resin-based hard carbon material; the protective atmosphere is the same as described above and will not be repeated here; the preferred temperature for the high-temperature treatment is 1300℃~1500℃; optionally, the temperature for the high-temperature treatment is 1300℃, 1350℃, 1400℃, 1450℃, 1500℃ or any two of the above values; the duration of the high-temperature treatment is 1~5 h; optionally, the duration of the high-temperature treatment is 1 h, 2 h, 3 h, 4 h, 5 h or any two of the above values.

[0042] The preparation method provided by this invention directly designs the structure based on the hard carbon material itself, without the need for complex coating or deposition processes, and is characterized by its simplicity. Furthermore, the closed-pore volume, interlayer spacing, and thickness of the carbon layers in the obtained hard carbon material can be precisely controlled by changing the amount of phosphoric acid added and the high-temperature heat treatment temperature and time, thereby enabling the prepared hard carbon material to have a rich closed-pore structure. It can be used as a negative electrode material for sodium-ion batteries, exhibiting excellent first coulombic efficiency, high plateau capacity, and high reversible specific capacity, thus significantly improving the electrochemical performance of sodium-ion batteries.

[0043] The present invention also provides a phenolic resin-based hard carbon material prepared by the above preparation method.

[0044] In one specific embodiment of the present invention, the carbon interlayer spacing of the phenolic resin-based hard carbon material is 0.37~0.40 nm.

[0045] The present invention also provides a sodium-ion battery, including a negative electrode; the negative electrode includes a phenolic resin-based hard carbon material prepared by the above preparation method.

[0046] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, provides a phenolic resin-based hard carbon material, its preparation method, and its application.

[0047] All reagents used in the following examples are commercially available; the phenolic resin used in the examples is prepared from resorcinol and formaldehyde, with a crosslinking degree of 83%.

[0048] Example 1

[0049] 1.1 Phenolic resin was carbonized at 500℃ for 3 h in an argon atmosphere with a heating rate of 10℃ / min to obtain RF-500.

[0050] 1.2 Disperse RF-500 in an ethanol-water mixture (ethanol to water volume ratio of 1:1), and add 10 wt% (mass ratio, m) 磷酸 :m RF-500The above mixture was then dried in a vacuum oven at 120°C for 10 h and carbonized at 600°C for 1 h under an argon atmosphere to obtain RF-500-P10.

[0051] 1.3 RF-500-P10% was washed with deionized water until neutral and dried in an oven at 80°C for 2 h to obtain purified RF-500-P10.

[0052] 1.4 The purified RF-500-P10% was subjected to high-temperature treatment at 1500℃ for 1 h in an argon atmosphere to obtain phenolic hard carbon material, denoted as RF-500-P10%HC.

[0053] Example 2

[0054] 2.1 Phenolic resin was carbonized at 900℃ for 1h in an argon atmosphere with a heating rate of 10℃ / min to obtain RF-900.

[0055] 2.2 Disperse RF-900 in a 1:1 volume ratio ethanol-water mixture, and add 10 wt% (mass ratio, m) 磷酸 :m RF-900 The above mixture was then dried in a vacuum oven at 120°C for 10 hours and carbonized at 600°C for 2 hours under an argon atmosphere to obtain RF-900-P10.

[0056] 2.3 RF-900-P10% was washed with deionized water until neutral and dried in an oven at 80°C for 2 h to obtain purified RF-900-P10.

[0057] 2.4 The purified RF-900-P10% was subjected to high-temperature treatment at 1500℃ for 1 h in an argon atmosphere to obtain phenolic hard carbon material, denoted as RF-900-P10%HC.

[0058] Example 3

[0059] 3.1 Phenolic resin was carbonized at 900℃ for 1h in an argon atmosphere with a heating rate of 10℃ / min to obtain RF-900.

[0060] 3.2 Disperse RF-900 in a 1:1 volume ratio ethanol-water mixture, and add 10 wt% (mass ratio, m) 磷酸 :m RF-900 Phosphoric acid (concentration of 85%) was added; then the above mixture was dried in a vacuum oven at 120°C for 10 h and carbonized at 400°C for 4 h under an argon atmosphere to obtain RF-900-P10%-1.

[0061] 3.3 RF-900-P10%-1 was washed with deionized water until neutral and dried in an oven at 80°C for 2 h to obtain purified RF-900-P10%-1.

[0062] 3.4 The purified RF-900-P10%-1 was subjected to high-temperature treatment at 1500℃ for 1 h in an argon atmosphere to obtain phenolic hard carbon material, denoted as RF-900-P10%HC-1.

[0063] Example 4

[0064] 4.1 Phenolic resin was carbonized at 900℃ for 1 h in an argon atmosphere with a heating rate of 10℃ / min to obtain RF-900.

[0065] 4.2 Disperse RF-900 in a 1:1 volume ratio ethanol-water mixture, and add 30 wt% (mass ratio, m) 磷酸 :m RF-900 The above mixture was then dried in a vacuum oven at 120°C for 10 h and carbonized at 600°C for 2 h under an argon atmosphere to obtain RF-900-P30.

[0066] 4.3 RF-900-P30% was washed with deionized water until neutral and dried in an oven at 80°C for 2 h to obtain purified RF-900-P30.

[0067] 4.4 The purified RF-900-P30% was subjected to high-temperature treatment at 1500℃ for 1 h in an argon atmosphere to obtain phenolic hard carbon material, denoted as RF-900-P30%HC.

[0068] Example 5

[0069] 5.1 Phenolic resin was carbonized at 900℃ for 1 h in an argon atmosphere with a heating rate of 10℃ / min to obtain RF-900.

[0070] 5.2 Disperse RF-900 in a 1:1 volume ratio ethanol-water mixture, and add 50 wt% (mass ratio, m) 磷酸 :m RF-900 The above mixture was then dried in a vacuum oven at 120°C for 10 h and carbonized at 600°C for 2 h under an argon atmosphere to obtain RF-900-P50.

[0071] 5.3 RF-900-P50% was washed with deionized water until neutral and dried in an oven at 80°C for 2 h to obtain purified RF-900-P50.

[0072] 5.4 The purified RF-900-P50% was subjected to high-temperature treatment at 1500℃ for 1 h in an argon atmosphere to obtain phenolic hard carbon material, denoted as RF-900-P50%HC.

[0073] The phenolic hard carbon material obtained in Example 5 was analyzed using scanning electron microscopy, and its scanning electron micrograph is shown below. Figure 1 As shown.

[0074] The phenolic-based hard carbon material obtained in Example 5 was analyzed using high-resolution transmission electron microscopy (TEM), and its high-resolution TEM image is shown below. Figure 2 As shown.

[0075] The phenolic-based hard carbon material obtained in Example 5 was analyzed using infrared spectroscopy, and its infrared spectrum is shown below. Figure 3 As shown.

[0076] Example 6

[0077] 6.1 Phenolic resin was carbonized at 900℃ for 1 h in an argon atmosphere with a heating rate of 10℃ / min to obtain RF-900.

[0078] 6.2 Disperse RF-900 in a 1:1 volume ratio ethanol-water mixture, and add 70 wt% (mass ratio, m) 磷酸 :m RF-900 The above mixture was then dried in a vacuum oven at 120°C for 10 h and carbonized at 600°C for 2 h under an argon atmosphere to obtain RF-900-P70.

[0079] 6.3 RF-900-P70% was washed with deionized water until neutral and dried in an oven at 80°C for 2 h to obtain purified RF-900-P70.

[0080] 6.4 The purified RF-900-P70% was subjected to high-temperature treatment at 1500℃ for 1 hour in an argon atmosphere to obtain phenolic hard carbon material, denoted as RF-900-P70%HC.

[0081] Example 7

[0082] The difference between this embodiment and Example 6 is that the high-temperature carbonization temperature is 1300℃. Apart from the above differences, the other experimental steps are the same as those in Example 6. The phenolic hard carbon material prepared in this way is denoted as RF-900-P70%HC-1.

[0083] Comparative Example 1

[0084] Phenolic resin was carbonized at 900℃ for 1 h in an argon atmosphere with a heating rate of 10℃ / min to obtain RF-900; RF-900 was then subjected to high-temperature treatment at 1500℃ for 1 h in an argon atmosphere to obtain phenolic-based hard carbon material denoted as RFHC.

[0085] Using the phenolic hard carbon materials obtained in Examples 1-6 and Comparative Example 1 as negative electrode materials, they were mixed and dispersed in deionized water solvent with conductive agent acetylene black and binder sodium alginate in a mass ratio of 8:1:1 to obtain a slurry with a solid content of 10%. The slurry was coated on the surface of the current collector copper foil, dried, and rolled to obtain a negative electrode sheet with an areal density of approximately 1.2 mg / cm³. 2 Compacted density 1.5 g / cm³ 3 .

[0086] A CR2032 button cell was assembled using sodium metal as the counter electrode, 1M NaPF6 dissolved in EC (ethylene carbonate) / DEC (diethyl carbonate) solvent (volume ratio 1:1), and glass fiber (porosity approximately 74.3%) as the separator, in an argon-protected glove box (water and oxygen content <0.1 ppm).

[0087] The electrochemical performance of the battery was tested using a constant current charge-discharge method (test voltage 2.8-0.001V, test current 0.02 A / g), and the comparison graph of its first charge-discharge cycle is shown below. Figure 4 As shown; a comparison chart of its slope capacity and platform capacity is obtained as follows. Figure 5 As shown.

[0088] To more intuitively demonstrate the performance of the materials prepared by this invention, Table 1 below lists the carbon layer structure data, closed-pore volume, and electrochemical performance of the anode materials prepared in each embodiment.

[0089] Where La is the width of the carbon microcrystals and Lc is the height of the carbon microcrystal stack.

[0090] Reversible specific capacity: Generally refers to the capacity that a battery can reversibly release in each cycle under a specific charge-discharge regime. Plateau capacity: The capacity discharged to below 0.1V; in this invention, it is the result of testing at a current density of 20 mA / s with the voltage range controlled between 2.8 and 0.001V.

[0091] Table 1 Performance test results of phenolic resin-based hard carbon materials

[0092]

[0093] From Table 1 and Figures 1-5It is known that the hard carbon material prepared by this invention has abundant closed-pore structure, and when used as a negative electrode material for sodium-ion batteries, it exhibits excellent first coulombic efficiency, high plateau capacity and high reversible specific capacity, thereby significantly improving the electrochemical performance of sodium-ion batteries.

[0094] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle 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 producing a phenolic resin-based hard carbon material, characterized by, The method comprises the following steps: S1) heating phenolic resin in a protective atmosphere to perform a first carbonization treatment to obtain a carbonized product; S2) mixing the carbonized product with phosphoric acid and performing a second carbonization treatment in a protective atmosphere to obtain a cross-linked carbonized product; S3) performing a purification treatment on the cross-linked carbonized product to remove phosphates to obtain a purified cross-linked carbonized product; S4) performing a high-temperature treatment on the purified cross-linked carbonized product in a protective atmosphere to obtain a phenolic resin-based hard carbon material.

2. The production method according to claim 1, characterized by, The heating rate in the step S1) is 5-15 ℃ / min; The temperature of the first carbonization treatment is 500-900 ℃, and the time of the first carbonization treatment is 1-3 h.

3. The preparation method according to claim 1, characterized in that, The mass concentration of the phosphoric acid is 80-85%; The mass of the phosphoric acid is 10-90% of the mass of the carbonized product.

4. The production method according to claim 1, characterized by, In the step S2), the carbonized product and the phosphoric acid are mixed in an ethanol aqueous solution, dried, and then subjected to the second carbonization treatment.

5. The method of claim 1, wherein, The temperature of the second carbonization treatment is 400-600 ℃, and the time of the second carbonization treatment is 1-4 h.

6. The method of claim 1, wherein, The purification treatment in the step S3) is specifically water washing and drying.

7. The preparation method according to claim 1, characterized in that, The temperature of the high-temperature treatment in the step S4) is 1300-1500 ℃, and the time of the high-temperature treatment is 1-5 h.

8. A phenolic resin-based hard carbon material prepared by the preparation method of any one of claims 1-7.

9. The phenolic resin-based hard carbon material according to claim 8, wherein The carbon layer spacing of the phenolic resin-based hard carbon material is 0.37-0.40 nm.

10. A sodium-ion battery, characterized in that, The negative electrode comprises the phenolic resin-based hard carbon material prepared by the preparation method of any one of claims 1-7.

Images