Coal-based phenolic resin-based hard carbon, and preparation method and application thereof

Abstract

The application provides coal-based phenolic resin-based hard carbon and a preparation method and application thereof, and belongs to the technical field of electrode materials, and aims to solve the technical problems of low specific capacity, low initial coulombic efficiency and poor cycle stability of phenolic resin-derived hard carbon.The preparation method of the coal-based phenolic resin-based hard carbon comprises the following steps: (1) adding coal powder into an activation solution for activation to obtain activated coal powder; (2) adding the activated coal powder into a mixed solution of formaldehyde and a phenolic monomer for prepolymerization to obtain liquid-phase phenolic resin; (3) adding the liquid-phase phenolic resin into a mixed solvent for solvothermal reaction to obtain coal-based phenolic resin; (4) crushing and sieving the coal-based phenolic resin, and then performing a carbonization process to obtain coal-based phenolic resin-based hard carbon; and (5) performing carbon coating treatment on the obtained hard carbon to obtain a final hard carbon product.The coal-based phenolic resin-based hard carbon prepared by the application has good particle size uniformity, and exhibits the characteristics of high specific capacity, high initial coulombic efficiency and long cycle stability in a sodium ion battery.

Description

Technical Field

[0001] This invention belongs to the technical field of electrode materials, and particularly relates to a coal-based phenolic resin-based hard carbon, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries (SIBs) are considered an excellent alternative to lithium-ion batteries due to their lower cost, better safety, superior high and low temperature performance, and suitability for grid-scale energy storage applications. However, because Na-C binary compounds are unstable, Na... + Graphite, widely used as an anode material in lithium-ion batteries, cannot be intercalated into sodium-ion batteries, making it unsuitable as a negative electrode material. Therefore, developing high-performance sodium-ion battery negative electrode materials is crucial for commercial application. Currently, sodium-ion battery negative electrode materials include carbon negative electrodes, alloy-based negative electrode materials, and conversion-based negative electrode materials. Among them, hard carbon (HC) is widely considered a potential negative electrode candidate for sodium-ion batteries due to its high specific surface area, high conductivity, low operating voltage plateau, high structural stability, abundant resources, and low cost. Due to its unique microstructure, hard carbon can effectively insert and remove sodium ions, exhibiting excellent sodium storage performance. Precursors for hard carbon preparation mainly include natural biomass materials, coal, and artificially synthesized phenolic resins. However, the availability of coal and biomass materials is dependent on their origin, resulting in poor controllability of the prepared hard carbon.

[0003] Phenolic resins, with their high carbon yield (~50%) and mature, controllable production technology, are considered one of the most promising precursors for preparing HC. However, HC derived from phenolic resins exhibits high structural regularity and low interlayer spacing, resulting in low initial coulombic efficiency (ICE) and limited sodium storage capacity, hindering its further commercial application. In recent years, researchers have conducted work on modifying the crosslinked structure of phenolic resins, such as through esterification, epoxy modification, and sucrose modification (ACS Energy Lett. 2024, 9(6), 2590-2614; Battery Energy, 2(2), 20220054; CN116605864A; CN115010109A). However, these methods require expensive raw materials and complex preparation processes, thus hindering the practical application of the hard carbon materials prepared in sodium-ion batteries.

[0004] Therefore, there is an urgent need for a simple, economical, green and environmentally friendly method for preparing hard carbon, which can improve the electrochemical performance of hard carbon anode materials, reduce surface defects of the materials, improve the first coulombic efficiency (ICE) of hard carbon materials, and obtain high-performance sodium-ion battery anode materials. Summary of the Invention

[0005] To address the technical problems of low initial coulombic efficiency and poor cycle stability of phenolic resin-derived hard carbon, this invention proposes a coal-based phenolic resin-based hard carbon, its preparation method, and its application. The prepared coal-based phenolic resin-based hard carbon has good particle size uniformity and exhibits high initial efficiency, high specific capacity, and long cycle stability in sodium-ion batteries.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A method for preparing coal-based phenolic resin-based hard carbon includes the following steps:

[0008] (1) The coal is crushed and sieved to obtain coal powder with a particle size of 200 mesh. The coal powder is added to hydrochloric acid solution for impurity removal. After ultrasonic cleaning, filtration and drying, the impurity-removed coal powder is obtained.

[0009] (2) Add the cleaned coal powder prepared in step (1) to the activation solution, stir continuously under heating conditions, and then cool, dilute, wash and dry to obtain activated coal powder;

[0010] (3) The activated coal powder obtained in step (2) is added to a mixed solution of formaldehyde and phenol monomers, and liquid-phase phenolic resin is obtained through prepolymerization reaction.

[0011] (4) The liquid phenolic resin obtained in step (3) is added to the mixed solvent, and the mixed solution is subjected to solvothermal reaction, centrifugation and drying to obtain coal-based phenolic resin.

[0012] (5) After crushing and sieving the coal-based phenolic resin obtained in step (4), coal-based phenolic resin-based hard carbon is obtained through pretreatment and calcination processes.

[0013] The coal mentioned in step (1) is one of anthracite, bituminous coal, sub-bituminous coal, and lignite.

[0014] Furthermore, in step (1), the concentration of the hydrochloric acid solution is 4-12 mol / L; the stirring temperature for impurity removal is 25℃ and the time is 6h; the solvent used for cleaning is deionized water, the drying temperature is 60℃, and the drying time is 4-12h.

[0015] The activation solution is nitric acid or sulfuric acid with a concentration of 2-6 mol / L; the activation temperature is 50-80℃, and the activation time is 4-12 h. The activation treatment of coal in step (2) increases the oxygen-containing functional groups on the surface of the coal, which is beneficial for the reaction with phenol monomers and formaldehyde to synthesize a network-structured coal-based phenolic resin. The addition of activated coal powder reduces the use of phenol, lowers the raw material cost, and changes the crosslinking degree of the phenolic resin, which is beneficial for the formation of micropores and mesopores during the preparation of hard carbon materials, and also beneficial for Na... + This improves the transmission capacity of its platform area.

[0016] The catalyst used for the prepolymerization reaction is sodium carbonate, ammonia, sodium hydroxide, and potassium hydroxide, and the amount used is 0.5-3% of the weight of the phenol monomer.

[0017] The phenolic monomer is one or more of phenol, bisphenol A, resorcinol or hydroquinone, and the molar ratio of the phenolic monomer to formaldehyde is 1:(1-3). Activated coal powder replaces 5-50 wt% of the phenolic monomer. The temperature of the prepolymerization reaction is 60-100℃ and the time is 2-6 h.

[0018] The mixed solvent includes water and an alcohol solvent, wherein the alcohol solvent is one or more of ethanol, propanol, or n-butanol; the volume ratio of water to alcohol solvent is 1:(0.75-1.5), and the volume ratio of liquid phenolic resin to mixed solvent is 1:(0.5-2); the temperature of the solvothermal reaction is 110-200℃, and the time is 10min-12h.

[0019] The particle size of the crushed coal-based phenolic resin in step (5) is 100-200 mesh; the carbonization process includes a pretreatment process and a calcination process.

[0020] The pretreatment process includes Stage I and Stage II. Stage I: In an inert gas, the temperature is raised to 100-300℃ at a rate of 2-10℃ / min and held at that temperature for 1-4 hours. Stage II: In an inert gas, the temperature is raised to 500-800℃ at a rate of 1-5℃ / min and activated at that temperature in an activating gas for 2-10 hours. The activating gas is at least one of water vapor and CO2.

[0021] The calcination process is as follows: in an inert gas atmosphere, the calcination temperature is 1000-1600℃, the holding time is 1-6h, and the heating rate is 1-5℃ / min.

[0022] The inert gas includes at least one of nitrogen and argon;

[0023] Furthermore, the coal-based phenolic resin-based hard carbon obtained in step (5) is impregnated, dried, and subjected to secondary carbonization in an organic compound solution to obtain a modified hard carbon material; the organic compound is one or more of coal tar, N-methylpyrrolidone, terpineol, polyvinylpyrrolidone, polyethylene oxide, or polyethylene glycol; the mass ratio of the organic compound to the hard carbon material is (0.05-0.5):1; the impregnation time is 2-6 hours, and the impregnation temperature is 40-80℃. Liquid-phase impregnation of carbon coating reduces surface defects in the hard carbon material, lowers the specific surface area of ​​the material, and thus improves the initial coulombic efficiency of the hard carbon material.

[0024] The secondary carbonization process is as follows: in an inert gas atmosphere, the calcination temperature is 1000-1600℃, the holding time is 1-6h, and the heating rate is 1-5℃ / min.

[0025] Furthermore, the particle size of the coal-based phenolic resin-based hard carbon is 6-15 μm.

[0026] Furthermore, the interlayer spacing of the coal-based phenolic resin-based hard carbon material (002) is 0.37-0.40 nm.

[0027] Application of a coal-based phenolic resin-based hard carbon in sodium / lithium-ion batteries and supercapacitors.

[0028] Beneficial effects of the present invention

[0029] 1. In this invention, a coal-based phenolic resin with a network cross-linked structure is formed through the condensation reaction of activated coal with phenolic monomers and formaldehyde. The resulting hard carbon material, after carbonization, possesses abundant micropores and mesopores, enabling it to accommodate more sodium ions and facilitate faster insertion / extraction, thus increasing sodium storage capacity. Further liquid-phase impregnation carbonization coating treatment reduces surface defects and specific surface area, increasing the initial coulombic efficiency of the hard carbon material. The hard carbon material prepared by this invention features uniform particle size, low specific surface area, abundant mesopores and micropores, and high structural stability. The abundant mesopores facilitate the storage of more sodium ions, resulting in higher volumetric energy density, lower specific surface area, reduced irreversible capacity loss, expanded plateau capacity, and increased initial coulombic efficiency.

[0030] 2. The sodium-ion battery using coal-based phenolic resin-based hard carbon as the negative electrode of this invention provides space for sodium-ion storage through the rich mesoporous structure of the hard carbon, thus expanding the platform capacity of the hard carbon material. The low specific surface area indicates fewer defects in the material, improving the initial coulombic efficiency. When this material is used as the negative electrode of a sodium-ion battery, the initial coulombic efficiency reaches 85.0%, the discharge capacity at a current density of 0.03 A / g is 399.48 mAh / g, and the initial discharge specific capacity at a current density of 0.2 A / g is 276.51 mAh / g, which decays to 274.63 mAh / g after 95 charge-discharge cycles, with a specific capacity retention rate of 99.3%. The resulting sodium-ion battery exhibits excellent electrochemical performance, including high initial coulombic efficiency, high specific capacity, and good cycle stability.

[0031] 3. The coal-based phenolic resin-based hard carbon material for sodium-ion batteries of the present invention is prepared by activating coal through a condensation reaction of coal with phenolic monomers and formaldehyde to form a network cross-linked coal-based phenolic resin, followed by carbonization. This hard carbon material possesses abundant micropores and mesopores, enabling it to accommodate more sodium ions and expanding its capacity plateau. Further liquid-phase impregnation carbonization coating treatment reduces surface defects, thereby improving the initial coulombic efficiency of the hard carbon material. The operation method is simple, yields high output, and has low cost, making it suitable for large-scale factory production.

[0032] 4. The hard carbon material with abundant mesoporous structure and low open pore specific surface area prepared by this invention is expected to have profound research significance and application prospects in fields such as supercapacitors, sodium / lithium-ion batteries, and catalysis. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 The X-ray diffraction (XRD) pattern of coal-based phenolic resin-based hard carbon material.

[0035] Figure 2 The images are scanning electron microscope (SEM) images of coal-based phenolic resin-based hard carbon materials. (ab) is the SEM of HC, and (cd) is the SEM of HC@C.

[0036] Figure 3 The specific surface area adsorption curve (BET) of coal-based phenolic resin-based hard carbon material is shown in (a) adsorption-desorption isotherm diagram and (b) pore size distribution diagram.

[0037] Figure 4 The first five constant current charge-discharge curves of a sodium-ion battery using coal-based phenolic resin-based hard carbon as the negative electrode material at a current density of 0.03 mAh / g.

[0038] Figure 5 Rate performance curve of a sodium-ion battery using coal-based phenolic resin-based hard carbon material as the negative electrode material.

[0039] Figure 6 Cycle stability curves of sodium-ion batteries using coal-based phenolic resin-based hard carbon materials as the negative electrode material. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1

[0042] A coal-based phenolic resin-based hard carbon, the preparation method of which includes the following steps:

[0043] (1) Weigh 20g of coal powder, add a small amount of ethanol to soak it, then add 50mL of HCl solution with a concentration of 4mol / L, stir at a constant temperature of 50℃ for 8h, filter the product, wash the precipitate with deionized water until neutral, and dry it under vacuum at 80℃ for 12h to obtain the purified coal powder.

[0044] (2) The purified coal powder obtained in step (1) above is added to 50 mL of HNO3 solution with a concentration of 4 mol / L. After stirring at a constant temperature of 60℃ for 12 h, the resulting product is filtered. The precipitate is washed with deionized water until neutral and dried under vacuum at 80℃ for 12 h to obtain activated coal powder.

[0045] (3) The activated coal powder obtained in step (2) above is added to a mixed solution of formaldehyde and phenol. The molar ratio of phenol to formaldehyde is 1:1.05, the amount of activated coal powder is 20% of the mass of phenol, and the amount of ammonia catalyst is 2%. The mixture is stirred continuously for 4 hours at a constant temperature of 80°C to obtain liquid phase coal-based phenolic resin.

[0046] (4) The liquid phase coal-based phenolic resin obtained in step (3) above is added to an ethanol solution with a volume ratio of 1:1 between the liquid phase phenolic resin and the ethanol solution. The mixture is then placed in a 100 mL autoclave with a polytetrafluoroethylene liner and sealed. The autoclave is kept at 180 °C for 5 h. After the reaction is complete, the product is centrifuged. The centrifuged precipitate is washed three times each with deionized water and anhydrous ethanol. The precipitate is then vacuum dried at 60 °C for 12 h to obtain solid phase coal-based phenolic resin material.

[0047] (5) The solid coal-based phenolic resin obtained in step (4) above is subjected to preliminary crushing and sieving treatment, and 100-mesh coal-based phenolic resin powder is retained.

[0048] (6) The coal-based phenolic resin obtained in step (5) above is transferred to a tube furnace for pretreatment to obtain pretreated hard carbon material; the pretreatment includes stage I and stage II. Stage I: in nitrogen, the temperature is raised to 300°C at a rate of 5°C / min and held for 2 hours; Stage II: in nitrogen, the temperature is raised to 800°C at a rate of 5°C / min and activated at a constant temperature in water vapor for 4 hours.

[0049] (7) The pretreated carbon material obtained in step (6) above is subjected to high-temperature carbonization in a tube furnace to obtain coal-based phenolic resin-based hard carbon material (HC); the carbonization temperature of the high-temperature carbonization treatment is 1400℃, the holding time is 4h, the heating rate is 2℃ / min, and the carbonization protective gas is nitrogen.

[0050] (8) The coal-based phenolic resin-based hard carbon obtained in step (7) above is added to an aqueous solution of N-methylpyrrolidone. The mass ratio of coal-based phenolic resin to N-methylpyrrolidone is 1:0.3, and the solid content of the N-methylpyrrolidone aqueous solution phase is 1.3g:10mL to the deionized water. After stirring at a constant temperature of 60℃ for 2h, the resulting product is dried under vacuum at 80℃ for 12h.

[0051] (9) The impregnated coal-based phenolic resin-based hard carbon obtained in step (8) above is carbonized again to obtain the final modified coal-based phenolic resin-based hard carbon material (HC@C); the carbonization temperature of the high-temperature carbonization treatment is 1400℃, the holding time is 4h, the heating rate is 2℃ / min, and the carbonization protective gas is nitrogen.

[0052] Figure 1 The XRD patterns of HC and HC@C prepared in Example 1 were compared with the XRD pattern of HC before coating. The amorphous peak of carbon on the (002) crystal plane of HC@C after coating shifted to the left, indicating that a carbon coating layer was successfully coated on the surface of HC@C.

[0053] Figure 2 SEM images of HC(ab) and HC@C(cd) prepared for Example 1 are shown. Compared with the XRD image of HC before coating, the surface of HC@C after coating is smoother.

[0054] Figure 3 BET curves of HC and HC@C were prepared for Example 1, wherein the specific surface area of ​​HC was 15.3 m². 2 g -1 The pore volume is 0.023 cm³. 3 g -1 The specific surface area of ​​HC@C is 4.93 m². 2 g -1 The pore volume is 0.011 cm³. 3 g -1Comparing the BET curve of HC before coating, it was found that the specific surface area of ​​HC@C after coating was reduced, indicating that the surface of HC@C has fewer defects.

[0055] Application Example 1

[0056] Sodium-ion batteries were assembled using the modified coal-based phenolic resin-based hard carbon materials (HC and HC@C) prepared in Example 1 as negative electrode materials. The preparation process of the half-cell was as follows: the self-made negative electrode sheet was composed of coal-based phenolic resin-based hard carbon, conductive agent (acetylene black), and binder (polyvinylidene fluoride) in a ratio of 8:1:1; the sodium-ion battery was assembled in a sealed glove box filled with argon gas, and the water content and oxygen content were controlled below 0.1 ppm; after the half-cell was assembled conventionally with a self-made circular electrode with a diameter of 12 mm as the negative electrode, a Celgard 2400 with a diameter of 17 mm as the separator, and a pure sodium sheet as the counter electrode, electrochemical tests were performed.

[0057] The charge-discharge curves of the sodium-ion battery obtained using the modified coal-based phenolic resin-based hard carbon material (HC@C) of this embodiment as the negative electrode material are as follows: Figure 4 As shown, Voltage (V) represents the voltage, and Specific capacity (mAh / g) represents the specific capacity. During this process, the charge-discharge curves did not change significantly, indicating that this coal-based phenolic resin-based hard carbon exhibits excellent stability as a negative electrode material in sodium-ion batteries.

[0058] The rate performance of sodium-ion batteries obtained using the modified coal-based phenolic resin-based hard carbon materials (HC and HC@C) as negative electrode materials in this embodiment is as follows: Figure 5As shown, from left to right, the discharge specific capacity data were measured under current densities of 0.03 A / g, 0.05 A / g, 0.1 A / g, 0.2 A / g, 0.5 A / g, 1.0 A / g, and 2.0 A / g. Cyclenumber represents the number of charge-discharge cycles, and Specific capacity (mAh / g) represents the charge-discharge specific capacity. The initial discharge specific capacity of HC was 415.98 mAh / g, the charge specific capacity was 303.67 mAh / g, the initial coulombic efficiency was 73.0%, and the plateau capacity ratio was 70.9%. After 5 cycles, the discharge specific capacity at a current density of 2 A / g was only 66.12 mAh / g, with the current densities of 0.03 A / g, 0.05 A / g, 0.1 A / g, 0.2 A / g, 0.5 A / g, 1.0 A / g, and 2.0 A / g being switched sequentially. The HC@C exhibits an initial discharge specific capacity of 469.73 mAh / g, a charge specific capacity of 399.48 mAh / g, an initial coulombic efficiency of 85.0%, and a plateau capacity of 75.1%. When the current density increases to 0.2 A / g, the specific capacity remains at 274.45 mAh / g. After five cycles at a current density of 2 A / g, when the current density is converted to 0.03 A / g, the specific capacity is approximately 398.24 mAh / g, representing 98% of the initial capacity, demonstrating good rate performance and cycle stability. Figure 5 The battery performance test results are shown in Table 1:

[0059] Table 1

[0060]

[0061]

[0062] The cycle stability curves of sodium-ion batteries obtained using the modified coal-based phenolic resin-based hard carbon materials as negative electrode materials in this embodiment are as follows: Figure 6 As shown in HC and HC@C. Figure 6 The HC curves show the charge-discharge data obtained after 5 and 95 charge-discharge cycles at current densities of 0.03 A / g and 0.2 A / g, respectively. At a current density of 0.2 A / g, the initial discharge specific capacity of HC is 218.24 mAh / g, which decays to 213.36 mAh / g after 95 charge-discharge cycles, with a specific capacity retention of 97.7%. Figure 6 The HC@C curves show the charge-discharge data obtained after 5 and 95 charge-discharge cycles at current densities of 0.03 A / g and 0.2 A / g, respectively. At a current density of 0.03 A / g, the initial discharge specific capacity was 276.51 mAh / g, which decreased to 274.63 mAh / g after 95 charge-discharge cycles, maintaining a specific capacity retention of 99.3%, demonstrating excellent cycle stability.

[0063] Example 2

[0064] A coal-based phenolic resin-based hard carbon, the preparation method of which includes the following steps:

[0065] (1) Weigh 20g of coal powder, add a small amount of ethanol to soak it, then add 50mL of HCl solution with a concentration of 4mol / L, stir at a constant temperature of 50℃ for 8h, filter the product, wash the precipitate with deionized water until neutral, and dry it under vacuum at 80℃ for 12h to obtain the purified coal powder.

[0066] (2) The purified coal powder obtained in step (1) above is added to 50 mL of HNO3 solution with a concentration of 4 mol / L. After stirring at a constant temperature of 60℃ for 12 h, the resulting product is filtered. The precipitate is washed with deionized water until neutral and dried under vacuum at 80℃ for 12 h to obtain activated coal powder.

[0067] (3) The activated coal powder obtained in step (2) above is added to a mixed solution of formaldehyde and phenol. The molar ratio of phenol to formaldehyde is 1:1.05, the amount of activated coal powder is 5% of the mass of phenol, and the amount of sodium hydroxide catalyst is 0.5%. The mixture is stirred continuously for 4 hours at a constant temperature of 70°C to obtain liquid phase coal-based phenolic resin.

[0068] (4) The liquid phase coal-based phenolic resin obtained in step (3) above is added to an ethanol solution with a volume ratio of 1:1 between the liquid phase phenolic resin and the ethanol solution. The mixture is then placed in a 100 mL autoclave with a polytetrafluoroethylene liner and sealed. The autoclave is kept at 180 °C for 12 h. After the reaction is complete, the product is centrifuged. The centrifuged precipitate is washed three times each with deionized water and anhydrous ethanol. The precipitate is then vacuum dried at 60 °C for 12 h to obtain the solid phase coal-based phenolic resin material.

[0069] (5) The solid coal-based phenolic resin obtained in step (4) above is subjected to preliminary crushing and sieving treatment, and 100-mesh coal-based phenolic resin powder is retained.

[0070] (6) The coal-based phenolic resin obtained in step (5) above is transferred to a tube furnace for pretreatment to obtain pretreated hard carbon material; the pretreatment includes stage I and stage II. Stage I: in nitrogen, the temperature is raised to 300°C at a rate of 5°C / min for 2 hours; Stage II: in nitrogen, the temperature is raised to 800°C at a rate of 5°C / min, and constant temperature activation is carried out in water vapor for 4 hours.

[0071] (7) The pretreated carbon material obtained in step (6) above is subjected to high-temperature carbonization in a tube furnace to obtain coal-based phenolic resin-based hard carbon material (HC-5%). The carbonization temperature of the high-temperature carbonization treatment is 1000℃, the holding time is 4h, the heating rate is 2℃ / min, and the carbonization protective gas is nitrogen.

[0072] (8) The coal-based phenolic resin-based hard carbon obtained in step (7) above is added to the coal tar solution. The mass ratio of coal-based phenolic resin to coal tar is 1:0.3, and the solid content of the coal tar solution phase is 1.3g:10mL to the deionized water. After stirring at 60℃ for 2h, the resulting product is vacuum dried at 80℃ for 12h.

[0073] (9) The impregnated coal-based phenolic resin-based hard carbon obtained in step (8) above is carbonized again to obtain the final modified coal-based phenolic resin-based hard carbon material (HC@C-5%); the carbonization temperature of the high-temperature carbonization treatment is 1000℃, the holding time is 4h, the heating rate is 2℃ / min, and the carbonization protective gas is nitrogen.

[0074] Application Example 2

[0075] Sodium-ion half-cells were assembled using the modified coal-based phenolic resin-based hard carbon (HC-5%) and HC@C-5%) materials prepared in Example 2 as negative electrode materials. The negative electrode sheet was composed of coal-based phenolic resin-based hard carbon, conductive agent, and binder in a ratio of 8:1:1. The assembly process was the same as in Application Example 1.

[0076] In this application example, HC-5% exhibits an initial discharge specific capacity of 294.45 mAh / g and a charge specific capacity of 205.31 mAh / g at a current density of 0.03 A / g, with an initial coulombic efficiency of 69.72%. At a current density of 0.2 A / g, the discharge specific capacity is 121.72 mAh / g, and after 100 charge-discharge cycles, the specific capacity retention is 95.37%. HC@C-5% exhibits an initial discharge specific capacity of 312.84 mAh / g and a charge specific capacity of 257.75 mAh / g at a current density of 0.03 A / g, with an initial coulombic efficiency of 82.39%. At a current density of 0.2 A / g, the discharge specific capacity is 173.17 mAh / g, and after 100 charge-discharge cycles, the specific capacity retention is 96.73%.

[0077] Example 3

[0078] A coal-based phenolic resin-based hard carbon, the preparation method of which includes the following steps:

[0079] (1) Weigh 20g of coal powder, add a small amount of ethanol to soak it, then add 50mL of HCl solution with a concentration of 4mol / L, stir at a constant temperature of 50℃ for 8h, filter the product, wash the precipitate with deionized water until neutral, and dry it under vacuum at 80℃ for 12h to obtain the purified coal powder.

[0080] (2) The purified coal powder obtained in step (1) above is added to 50 mL of HNO3 solution with a concentration of 4 mol / L. After stirring at a constant temperature of 60℃ for 12 h, the resulting product is filtered. The precipitate is washed with deionized water until neutral and dried under vacuum at 80℃ for 12 h to obtain activated coal powder.

[0081] (3) The activated coal powder obtained in step (2) above is added to a mixed solution of formaldehyde and phenol. The molar ratio of phenol to formaldehyde is 1:1.05, the amount of activated coal powder is 10% of the mass of phenol, and the amount of potassium hydroxide catalyst is 0.6%. The mixture is stirred continuously for 4 hours at a constant temperature of 60°C to obtain liquid phase coal-based phenolic resin.

[0082] (4) The liquid phase coal-based phenolic resin obtained in step (3) above is added to an ethanol solution with a volume ratio of 1:1 between the liquid phase phenolic resin and the ethanol solution. The mixture is then placed in a 100 mL autoclave with a polytetrafluoroethylene liner and sealed. The autoclave is kept at 180 °C for 12 h. After the reaction is complete, the product is centrifuged. The centrifuged precipitate is washed three times each with deionized water and anhydrous ethanol. The precipitate is then vacuum dried at 60 °C for 12 h to obtain the solid phase coal-based phenolic resin material.

[0083] (5) The solid coal-based phenolic resin obtained in step (4) above is subjected to preliminary crushing and sieving treatment, and 100-mesh coal-based phenolic resin powder is retained.

[0084] (6) The coal-based phenolic resin obtained in step (5) above is transferred to a tube furnace for pretreatment to obtain pretreated hard carbon material; the pretreatment includes stage I and stage II. Stage I: in nitrogen, the temperature is raised to 300°C at a rate of 5°C / min for 2 hours; Stage II: in nitrogen, the temperature is raised to 800°C at a rate of 5°C / min, and constant temperature activation is carried out in water vapor for 4 hours.

[0085] (7) The pretreated carbon material obtained in step (6) above is subjected to high-temperature carbonization in a tube furnace to obtain coal-based phenolic resin-based hard carbon material (HC-10%). The carbonization temperature of the high-temperature carbonization treatment is 1200℃, the holding time is 4h, the heating rate is 2℃ / min, and the carbonization protective gas is nitrogen.

[0086] (8) The coal-based phenolic resin-based hard carbon obtained in step (7) above is added to a polyvinylpyrrolidone aqueous solution. The mass ratio of coal-based phenolic resin to polyvinylpyrrolidone is 1:0.1, and the solid content of the polyvinylpyrrolidone aqueous solution phase is 1.3g:10mL to the deionized water. After stirring at 60℃ for 2h, the resulting product is vacuum dried at 80℃ for 12h.

[0087] (9) The impregnated coal-based phenolic resin-based hard carbon obtained in step (8) above is carbonized again to obtain the final modified coal-based phenolic resin-based hard carbon material (HC@C-10%); the carbonization temperature of the high-temperature carbonization treatment is 1200℃, the holding time is 4h, the heating rate is 2℃ / min, and the carbonization protective gas is nitrogen.

[0088] Application Example 3

[0089] Sodium-ion half-cells were assembled using the modified coal-based phenolic resin-based hard carbon materials (HC-10% and HC@C-10%) prepared in Example 3 as negative electrode materials. The negative electrode sheet was composed of coal-based phenolic resin-based hard carbon, conductive agent, and binder in a ratio of 8:1:1. The assembly process was the same as in Example 1.

[0090] In this application example, HC-10% exhibits an initial discharge specific capacity of 310.49 mAh / g and a charge specific capacity of 230.31 mAh / g at a current density of 0.03 A / g, with an initial coulombic efficiency of 74.17%. At a current density of 0.2 A / g, the discharge specific capacity is 134.61 mAh / g, and the capacity retention after 100 charge-discharge cycles is 95.86%. HC@C-10% exhibits an initial discharge specific capacity of 326.52 mAh / g and a charge specific capacity of 277.12 mAh / g at a current density of 0.03 A / g, with an initial coulombic efficiency of 84.87%. At a current density of 0.2 A / g, the discharge specific capacity is 194.80 mAh / g, and the capacity retention after 100 charge-discharge cycles is 97.48%.

[0091] Example 4

[0092] A coal-based phenolic resin-based hard carbon, the preparation method of which includes the following steps:

[0093] (1) Weigh 20g of coal powder, add a small amount of ethanol to soak it, then add 50mL of HCl solution with a concentration of 4mol / L, stir at a constant temperature of 50℃ for 8h, filter the product, wash the precipitate with deionized water until neutral, and dry it under vacuum at 80℃ for 12h to obtain the purified coal powder.

[0094] (2) The purified coal powder obtained in step (1) above is added to 50 mL of HNO3 solution with a concentration of 4 mol / L. After stirring at a constant temperature of 60℃ for 12 h, the resulting product is filtered. The precipitate is washed with deionized water until neutral and dried under vacuum at 80℃ for 12 h to obtain activated coal powder.

[0095] (3) The activated coal powder obtained in step (2) above is added to a mixed solution of formaldehyde and phenol. The molar ratio of phenol to formaldehyde is 1:1.05, the amount of activated coal powder is 30% of the mass of phenol, and the amount of sodium carbonate catalyst is 1.5%. The mixture is stirred continuously for 4 hours at a constant temperature of 60°C to obtain liquid phase coal-based phenolic resin.

[0096] (4) The liquid phase coal-based phenolic resin obtained in step (3) above is added to an ethanol solution with a volume ratio of 1:1 between the liquid phase phenolic resin and the ethanol solution. The mixture is then placed in a 100 mL autoclave with a polytetrafluoroethylene liner and sealed. The autoclave is kept at 180 °C for 12 h. After the reaction is complete, the product is centrifuged. The centrifuged precipitate is washed three times each with deionized water and anhydrous ethanol. The precipitate is then vacuum dried at 60 °C for 12 h to obtain the solid phase coal-based phenolic resin material.

[0097] (5) The solid coal-based phenolic resin obtained in step (4) above is subjected to preliminary crushing and sieving treatment, and 100-mesh coal-based phenolic resin powder is retained.

[0098] (6) The coal-based phenolic resin obtained in step (5) above is transferred to a tube furnace for pretreatment to obtain pretreated hard carbon material; the pretreatment includes stage I and stage II. Stage I: in nitrogen, the temperature is raised to 300°C at a rate of 5°C / min for 2 hours; Stage II: in nitrogen, the temperature is raised to 800°C at a rate of 5°C / min, and constant temperature activation is carried out in water vapor for 4 hours.

[0099] (7) The pretreated carbon material obtained in step (6) above is subjected to high-temperature carbonization in a tube furnace to obtain coal-based phenolic resin-based hard carbon material (HC-30%). The carbonization temperature of the high-temperature carbonization treatment is 1600℃, the holding time is 4h, the heating rate is 2℃ / min, and the carbonization protective gas is nitrogen.

[0100] (8) The coal-based phenolic resin-based hard carbon obtained in step (7) above is added to the polyethylene oxide aqueous solution. The mass ratio of coal-based phenolic resin to polyethylene oxide is 1:0.3, and the solid content of the polyethylene oxide aqueous solution phase is 1.3g:10mL to the deionized water. After stirring at 60℃ for 2h, the resulting product is vacuum dried at 80℃ for 12h.

[0101] (9) The impregnated coal-based phenolic resin-based hard carbon obtained in step (8) above is carbonized again to obtain the final modified coal-based phenolic resin-based hard carbon material (HC@C-30%); the carbonization temperature of the high-temperature carbonization treatment is 1600℃, the holding time is 4h, the heating rate is 2℃ / min, and the carbonization protective gas is nitrogen.

[0102] Application Example 4

[0103] Sodium-ion half-cells were assembled using the modified coal-based phenolic resin-based hard carbon materials (HC-30% and HC@C-30%) prepared in Example 4 as negative electrode materials. The negative electrode sheet was composed of coal-based phenolic resin-based hard carbon, conductive agent, and binder in a ratio of 8:1:1. The assembly process was the same as in Example 1.

[0104] In this application example, HC-30% exhibits an initial discharge specific capacity of 384.49 mAh / g and a charge specific capacity of 264.34 mAh / g at a current density of 0.03 A / g, with an initial coulombic efficiency of 68.75%. At a current density of 0.2 A / g, the discharge specific capacity is 189.25 mAh / g, and after 100 charge-discharge cycles, the specific capacity retention is 96.37%. HC@C-30% exhibits an initial discharge specific capacity of 361.21 mAh / g and a charge specific capacity of 302.33 mAh / g at a current density of 0.03 A / g, with an initial coulombic efficiency of 83.70%. At a current density of 0.2 A / g, the discharge specific capacity is 246.73 mAh / g, and after 100 charge-discharge cycles, the specific capacity retention is 98.74%.

[0105] Example 5

[0106] A coal-based phenolic resin-based hard carbon, the preparation method of which includes the following steps:

[0107] (1) Weigh 20g of coal powder, add a small amount of ethanol to soak it, then add 50mL of HCl solution with a concentration of 4mol / L, stir at a constant temperature of 50℃ for 8h, filter the product, wash the precipitate with deionized water until neutral, and dry it under vacuum at 80℃ for 12h to obtain the purified coal powder.

[0108] (2) Add the cleaned coal powder obtained in step (1) above to 50 mL of HNO3 solution with a concentration of 2 mol / L. Stir at 80℃ for 8 h. Filter the product and wash the precipitate with deionized water until neutral. Dry it under vacuum at 80℃ for 12 h to obtain activated coal powder.

[0109] (3) The activated coal powder obtained in step (2) above is added to a mixed solution of formaldehyde and phenol. The molar ratio of phenol to formaldehyde is 1:1.5, the amount of activated coal powder is 20% of the mass of phenol, and the amount of sodium hydroxide catalyst is 0.7%. The mixture is stirred continuously for 6 hours at a constant temperature of 100℃ to obtain liquid phase coal-based phenolic resin.

[0110] (4) The liquid phase coal-based phenolic resin obtained in step (3) above is added to an ethanol solution with a volume ratio of 1:2 between the liquid phase phenolic resin and the ethanol solution. The mixture is then placed in a 100 mL autoclave with a polytetrafluoroethylene liner and sealed. The autoclave is kept at 200 °C for 4 h. After the reaction is complete, the product is centrifuged. The centrifuged precipitate is washed three times each with deionized water and anhydrous ethanol. The precipitate is then vacuum dried at 60 °C for 12 h to obtain the solid phase coal-based phenolic resin material.

[0111] (5) The solid coal-based phenolic resin obtained in step (4) above is subjected to preliminary crushing and sieving treatment, and 150-mesh coal-based phenolic resin powder is retained.

[0112] (6) The coal-based phenolic resin obtained in step (5) above is transferred to a tube furnace for pretreatment to obtain pretreated hard carbon material; the pretreatment includes stage I and stage II. Stage I: in nitrogen, the temperature is raised to 200°C at a rate of 10°C / min for 2 hours; Stage II: in nitrogen, the temperature is raised to 500°C at a rate of 1°C / min, and constant temperature activation is carried out in water vapor for 10 hours.

[0113] (7) The pretreated carbon material obtained in step (6) above is subjected to high-temperature carbonization in a tube furnace to obtain coal-based phenolic resin-based hard carbon material (HC-20%-1.5); the carbonization temperature of the high-temperature carbonization treatment is 1200℃, the holding time is 1h, the heating rate is 5℃ / min, and the carbonization protective gas is nitrogen.

[0114] (8) The coal-based phenolic resin-based hard carbon obtained in step (7) above is added to the polyethylene oxide aqueous solution. The mass ratio of coal-based phenolic resin to polyethylene oxide is 1:0.1, and the solid content of the polyethylene oxide aqueous solution is 1.3g:10mL to the deionized water. After stirring at 40℃ for 4h, the resulting product is vacuum dried at 80℃ for 12h.

[0115] (9) The impregnated coal-based phenolic resin-based hard carbon obtained in step (8) above is carbonized again to obtain the final modified coal-based phenolic resin-based hard carbon material (HC@C-20%-1.5); the carbonization temperature of the high-temperature carbonization treatment is 1400℃, the holding time is 6h, the heating rate is 5℃ / min, and the carbonization protective gas is nitrogen.

[0116] Application Example 5

[0117] The modified coal-based phenolic resin-based hard carbon (HC-20%-1.5 and HC@C-20%-1.5) materials prepared in Example 5 were used as negative electrode materials to assemble sodium-ion half-cells. The negative electrode sheet was composed of coal-based phenolic resin-based hard carbon, conductive agent and binder in a ratio of 8:1:1. The assembly process was the same as in Example 1.

[0118] In this application example, HC-20%-1.5 exhibits an initial discharge specific capacity of 326.19 mAh / g and a charge specific capacity of 243.45 mAh / g at a current density of 0.03 A / g, with an initial coulombic efficiency of 74.63%. At a current density of 0.2 A / g, the discharge specific capacity is 167.53 mAh / g, and after 100 charge-discharge cycles, the specific capacity retention is 96.62%. HC@C-20%-1.5, at a current density of 0.03 A / g, exhibits an initial discharge specific capacity of 346.82 mAh / g and a charge specific capacity of 283.45 mAh / g, with an initial coulombic efficiency of 81.72%. At a current density of 0.2 A / g, the discharge specific capacity is 223.46 mAh / g, and after 100 charge-discharge cycles, the specific capacity retention is 97.54%.

[0119] Example 6

[0120] A coal-based phenolic resin-based hard carbon, the preparation method of which includes the following steps:

[0121] (1) Weigh 20g of coal powder, add a small amount of ethanol to soak it, then add 50mL of HCl solution with a concentration of 4mol / L, stir at a constant temperature of 50℃ for 8h, filter the product, wash the precipitate with deionized water until neutral, and dry it under vacuum at 80℃ for 12h to obtain the purified coal powder.

[0122] (2) Add the cleaned coal powder obtained in step (1) above to 50 mL of HNO3 solution with a concentration of 6 mol / L. Stir at 50℃ for 4 h. Filter the product and wash the precipitate with deionized water until neutral. Dry it under vacuum at 80℃ for 12 h to obtain activated coal powder.

[0123] (3) The activated coal powder obtained in step (2) above is added to a mixed solution of formaldehyde and phenol. The molar ratio of phenol to formaldehyde is 1:2, the amount of activated coal powder is 20% of the mass of phenol, and the amount of sodium carbonate catalyst is 1.5%. The mixture is stirred continuously for 6 hours at a constant temperature of 80°C to obtain liquid phase coal-based phenolic resin.

[0124] (4) The liquid phase coal-based phenolic resin obtained in step (3) above is added to an ethanol solution with a volume ratio of 1:0.5 between the liquid phase phenolic resin and the ethanol solution. The mixture is then placed in a 100 mL autoclave with a polytetrafluoroethylene liner and sealed. The autoclave is kept at 160 °C for 8 h. After the reaction is complete, the product is centrifuged. The centrifuged precipitate is washed three times each with deionized water and anhydrous ethanol. The precipitate is then vacuum dried at 60 °C for 12 h to obtain the solid phase coal-based phenolic resin material.

[0125] (5) The solid coal-based phenolic resin obtained in step (4) above is subjected to preliminary crushing and sieving treatment, and 200-mesh coal-based phenolic resin powder is retained.

[0126] (6) The coal-based phenolic resin obtained in step (5) above is transferred to a tube furnace for pretreatment to obtain pretreated hard carbon material; the pretreatment includes stage I and stage II. Stage I: in nitrogen, the temperature is raised to 100°C at a rate of 2°C / min for 4 hours; Stage II: in nitrogen, the temperature is raised to 600°C at a rate of 5°C / min, and constant temperature activation is carried out in CO2 for 2 hours.

[0127] (7) The pretreated carbon material obtained in step (6) above is subjected to high-temperature carbonization in a tube furnace to obtain coal-based phenolic resin-based hard carbon material (HC-20%-2.0); the carbonization temperature of the high-temperature carbonization treatment is 1000℃, the holding time is 6h, the heating rate is 1℃ / min, and the carbonization protective gas is nitrogen.

[0128] (8) The coal-based phenolic resin-based hard carbon obtained in step (7) above is added to the polyethylene oxide aqueous solution. The mass ratio of coal-based phenolic resin to polyethylene oxide is 1:0.5, and the solid content of the polyethylene oxide aqueous solution is 1.3g:10mL to the deionized water. After stirring at 60℃ for 2h, the resulting product is vacuum dried at 80℃ for 12h.

[0129] (9) The impregnated coal-based phenolic resin-based hard carbon obtained in step (8) above is carbonized again to obtain the final modified coal-based phenolic resin-based hard carbon material (HC@C-20%-2.0); the carbonization temperature of the high-temperature carbonization treatment is 1000℃, the holding time is 4h, the heating rate is 2℃ / min, and the carbonization protective gas is nitrogen.

[0130] Application Example 6

[0131] The modified coal-based phenolic resin-based hard carbon (HC-20%-2.0 and HC@C-20%-2.0) materials prepared in Example 6 were used as negative electrode materials to assemble sodium-ion half-cells. The negative electrode sheet was composed of coal-based phenolic resin-based hard carbon, conductive agent and binder in a ratio of 8:1:1. The assembly process was the same as in Example 1.

[0132] In this application example, HC-20%-2.0 exhibits an initial discharge specific capacity of 397.54 mAh / g and a charge specific capacity of 264.34 mAh / g at a current density of 0.03 A / g, with an initial coulombic efficiency of 66.49%. At a current density of 0.2 A / g, the discharge specific capacity is 177.47 mAh / g, and after 100 charge-discharge cycles, the capacity retention is 96.46%. HC@C-20%-2.0, at a current density of 0.03 A / g, exhibits an initial discharge specific capacity of 381.39 mAh / g and a charge specific capacity of 320.56 mAh / g, with an initial coulombic efficiency of 84.05%. At a current density of 0.2 A / g, the discharge specific capacity is 243.46 mAh / g, and after 100 charge-discharge cycles, the capacity retention is 97.39%.

[0133] Comparative Example 1

[0134] (1) Phenol and formaldehyde are mixed in a molar ratio of 1:1.05, and 2% ammonia water catalyst is added. The mixture is stirred continuously at a constant temperature of 80℃ for 4 hours to obtain liquid-phase phenolic resin.

[0135] (2) The liquid phenolic resin obtained in step (1) above is added to an ethanol solution with a volume ratio of 1:1. The solution is placed in a 100mL autoclave with a polytetrafluoroethylene liner and sealed. The autoclave is kept at 180℃ for 5 hours. After the reaction is completed, the product is centrifuged. The centrifuged precipitate is washed three times each with deionized water and anhydrous ethanol. The product is then vacuum dried at 60℃ for 12 hours to obtain a separate solid phenolic resin material.

[0136] (3) The solid phenolic resin obtained in step (2) above is subjected to preliminary crushing and sieving treatment, and 100-mesh solid phenolic resin powder is retained.

[0137] (4) The phenolic resin obtained in step (3) above is transferred to a tube furnace for pretreatment to obtain pretreated hard carbon material; the pretreatment includes stage I and stage II. Stage I: in nitrogen, the temperature is raised to 300°C at a rate of 5°C / min for 2 hours; Stage II: in nitrogen, the temperature is raised to 800°C at a rate of 5°C / min, and constant temperature activation is carried out in water vapor for 4 hours.

[0138] (5) The pretreated carbon material obtained in step (4) above is subjected to high-temperature carbonization in a tube furnace to obtain a single phenolic resin-based hard carbon material (HC-0%). The carbonization temperature of the high-temperature carbonization treatment is 1400℃, the holding time is 4h, the heating rate is 2℃ / min, and the carbonization protective gas is nitrogen.

[0139] (6) Add the phenolic resin-based hard carbon obtained in step (5) above to an aqueous solution of N-methylpyrrolidone. The mass ratio of coal-based phenolic resin to polymethylpyrrolidone is 1:0.3, and the solid content of the N-methylpyrrolidone aqueous solution phase to deionized water is 1.3g:10mL. After stirring at a constant temperature of 60℃ for 2h, the resulting product is vacuum dried at 80℃ for 12h.

[0140] (7) The impregnated phenolic resin-based hard carbon obtained in step (6) above is carbonized again to obtain the final modified coal-based phenolic resin-based hard carbon material (HC@C-0%); the carbonization temperature of the high-temperature carbonization treatment is 1400℃, the holding time is 4h, the heating rate is 2℃ / min, and the carbonization protective gas is nitrogen.

[0141] Comparative Application Example 1

[0142] Sodium-ion half-cells were assembled using the modified and unmodified phenolic resin-based hard carbon (HC-0%) and HC@C-0%) materials prepared in Comparative Example 1 as negative electrode materials. The negative electrode sheet was composed of coal-based phenolic resin-based hard carbon, conductive agent, and binder in a ratio of 8:1:1. The assembly process was the same as in Example 1.

[0143] In this application example, HC-0% exhibits an initial discharge specific capacity of 248.34 mAh / g and a charge specific capacity of 164.58 mAh / g at a current density of 0.03 A / g, with an initial coulombic efficiency of 66.27%. However, its discharge specific capacity at a current density of 0.2 A / g is only 52.1 mAh / g. HC@C-0% exhibits an initial discharge specific capacity of 251.65 mAh / g and a charge specific capacity of 205.80 mAh / g at a current density of 0.03 A / g, with an initial coulombic efficiency of 81.8%. However, its discharge specific capacity at a current density of 0.2 A / g is only 74.2 mAh / g, demonstrating low discharge specific capacity performance and poor rate charge / discharge performance.

[0144] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing coal-based phenolic resin-based hard carbon, characterized in that, Includes the following steps: (1) Coal powder is added to an activation solution to activate it, thereby obtaining activated coal powder; the activation solution is nitric acid or sulfuric acid with a concentration of 2-6 mol / L; the activation temperature is 50-80℃ and the activation time is 4-12 h; (2) Activated coal powder is added to a mixed solution of formaldehyde and phenolic monomers, and liquid-phase phenolic resin is obtained through prepolymerization reaction; the molar ratio of phenolic monomers to formaldehyde is 1:(1-3), and activated coal powder replaces 5-50 wt% of the phenolic monomers; the catalyst for the prepolymerization reaction is sodium carbonate, ammonia, sodium hydroxide or potassium hydroxide, and the amount used is 0.5-3% of the weight of phenolic monomers; the temperature of the prepolymerization reaction is 60-100℃, and the time is 2-6 h; (3) Liquid phenolic resin is added to a mixed solvent to carry out a solvothermal reaction to obtain coal-based phenolic resin; (4) After crushing and sieving coal-based phenolic resin, coal-based phenolic resin-based hard carbon is obtained by carbonization process.

2. The method for preparing coal-based phenolic resin-based hard carbon according to claim 1, characterized in that, The mixed solvent includes water and an alcohol solvent, wherein the alcohol solvent is one or more of ethanol, propanol, or n-butanol; the volume ratio of water to alcohol solvent is 1:(0.75-1.5), and the volume ratio of liquid phenolic resin to mixed solvent is 1:(0.5-2); the temperature of the solvothermal reaction is 110-200℃, and the time is 10 min-12 h.

3. The method for preparing coal-based phenolic resin-based hard carbon according to claim 2, characterized in that, The particle size of the crushed coal-based phenolic resin in step (4) is 100-200 mesh; the carbonization process includes a pretreatment process and a calcination process.

4. The method for preparing coal-based phenolic resin-based hard carbon according to claim 3, characterized in that, The pretreatment process includes Stage I and Stage II. Stage I: In an inert gas, the temperature is raised to 100-300℃ at a rate of 2-10℃ / min and held at that temperature for 1-4 h. Stage II: In an inert gas, the temperature is raised to 500-800℃ at a rate of 1-5℃ / min and activated at that temperature in an activating gas for 2-10 h. The activating gas is water vapor and / or CO2.

5. The method for preparing coal-based phenolic resin-based hard carbon according to claim 4, characterized in that, The calcination process is as follows: in an inert gas atmosphere, the calcination temperature is 1000-1600℃, the holding time is 1-6 h, and the heating rate is 1-5℃ / min.

6. The method for preparing coal-based phenolic resin-based hard carbon according to any one of claims 1-5, characterized in that, The coal-based phenolic resin-based hard carbon obtained in step (4) is impregnated in an organic compound solution and then subjected to secondary carbonization to obtain a modified hard carbon material. The organic compound is one or more of coal tar, N-methylpyrrolidone, terpineol, polyvinylpyrrolidone, polyethylene oxide, or polyethylene glycol. The mass ratio of the organic compound to the hard carbon material is (0.05-0.5):

1. The impregnation time is 2-6 h and the impregnation temperature is 40-80℃.

7. The coal-based phenolic resin-based hard carbon prepared by the method according to any one of claims 1-6, characterized in that, The particle size of the hard carbon material is 6-15 μm.

8. The application of the coal-based phenolic resin-based hard carbon according to claim 7 in the fields of sodium / lithium-ion batteries and supercapacitors.

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