Preparation method of composite hard carbon material, composite hard carbon material and sodium ion battery

Abstract

The invention provides a preparation method of a composite hard carbon material, the composite hard carbon material and a sodium ion battery. The preparation method comprises the following steps: adding carbon nanotubes and carbon black into a water-containing first solvent, carrying out ultrasonic treatment, and adding a silane coupling agent to carry out silanization reaction; dissolving phenolic resin and coal tar in a second solvent, adding a composite conductive agent, dispersing, and carrying out heat treatment and aging treatment; carbonizing the first precursor for the first time, crushing to obtain ground powder, and purifying the ground powder; and performing secondary carbonization on the second precursor. According to the preparation method, carbon nanotubes and carbon black serve as composite conductive agents and are subjected to co-silanization to construct a three-dimensional conductive network, phenolic resin and coal tar are compounded to serve as a carbon source to induce asynchronous shrinkage so as to enlarge the interlayer spacing of hard carbon, and then a hydrolysate of a silane coupling agent serves as a pore-forming template; and triple collaborative optimization of carbon layer spacing, graded pores and a conductive network of the hard carbon can be realized, so that the prepared composite hard carbon material has relatively good electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of new energy material preparation technology, and in particular to a method for preparing composite hard carbon materials, composite hard carbon materials and sodium-ion batteries. Background Technology

[0002] Sodium-ion batteries are considered an important alternative to lithium-ion batteries in large-scale energy storage due to the abundance and low cost of sodium resources. Hard carbon materials, with their large interlayer spacing and abundant defects, are among the most promising anode materials for sodium-ion batteries. Resin-based hard carbon, especially phenolic resin-based hard carbon, is attracting more attention due to its highly tunable structure and strong carbon-forming ability.

[0003] However, traditional resin-based hard carbon has the following problems: First, its carbon interlayer spacing (d002) is usually only in the range of 0.37~0.39 nm, which limits the storage sites of sodium ions and the insertion / extraction kinetics, resulting in room for improvement in specific capacity; second, its conductivity is poor; and third, unreasonable pore structure (such as too many openings) will lead to low initial coulombic efficiency and poor rate performance.

[0004] Existing technologies have attempted to improve performance through template-based pore creation or simple compounding with conductive agents (such as carbon black). However, these methods often struggle to effectively control the fundamental structural parameter of carbon interlayer spacing and are prone to uneven dispersion of the conductive agent or deterioration of the pore structure. In constructing conductive networks, while single zero-dimensional carbon black particles can provide point contact, their long-range conductivity is limited. Carbon nanotubes (CNTs), with their one-dimensional nanostructure and extremely high intrinsic conductivity, are ideal conductive additives. However, CNTs are prone to entanglement and aggregation, making uniform dispersion in the matrix difficult. Simply physically mixing CNTs with carbon black still results in uneven dispersion and high interfacial impedance due to differences in their surface properties. More importantly, the carbon interlayer spacing (d002) of existing hard carbon materials is mostly between 0.37 and 0.39 nm, limiting the storage sites and insertion / extraction kinetics of sodium ions. Although there are reports of layer expansion through heteroatom doping, these methods are often complex or lead to a decrease in initial efficiency.

[0005] Therefore, developing a simple method that can simultaneously achieve effective expansion of carbon layer spacing, controllable hierarchical pore structure, and construction of a highly efficient three-dimensional conductive network is the key to breaking through the current performance bottleneck. Summary of the Invention

[0006] In view of the above problems, the purpose of this invention is to provide a method for preparing composite hard carbon materials, the composite hard carbon materials, and a sodium-ion battery. The preparation method of this invention uses carbon nanotubes and carbon black as composite conductive agents and co-silanizes them to construct a three-dimensional conductive network. A composite of phenolic resin and coal tar is used as a carbon source to induce asynchronous shrinkage, thereby expanding the interlayer spacing of the hard carbon. Then, the hydrolysis products of a silane coupling agent are used as a pore-forming template. This achieves a triple synergistic optimization of the carbon interlayer spacing, hierarchical pore size, and conductive network of the hard carbon, thus resulting in a composite hard carbon material with superior electrochemical performance.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a composite hard carbon material, comprising the steps of: (I) Preparation of composite conductive agent Carbon nanotubes and carbon black were added to a first solvent containing water and ultrasonically treated. Then, a silane coupling agent was added to carry out a silanization reaction. (II) Preparation of the first precursor Phenolic resin and coal tar are dissolved in a second solvent, and the composite conductive agent is added and dispersed before heat treatment and aging treatment. (III) Preparation of the second precursor The first precursor is carbonized for the first time and then crushed to obtain a grinding powder. The grinding powder is purified, and the purification includes at least one of alkali washing, acid washing and water washing. (IV) High temperature carbonization The second precursor is carbonized a second time at a temperature higher than that of the first carbonization.

[0008] The preparation method of the present invention has at least the following technical effects.

[0009] (1) Using carbon nanotubes and carbon black as composite conductive agents, zero-dimensional carbon black (CB) can provide a large number of "point" contacts, while one-dimensional carbon nanotubes (CNTs) act as "bridges" to construct long-range electronic conduction pathways throughout the entire material. This three-dimensional network combining "points and lines" solves the inherent defects of single conductive agents, resulting in extremely high conductivity of composite hard carbon materials, which can provide excellent rate performance when used in batteries.

[0010] (2) A composite of phenolic resin and coal tar is used as the carbon source. The difference in thermal behavior between the rigid skeleton formed by phenolic resin (thermosetting) and the rapid shrinkage of coal tar (thermoplastic) during carbonization produces a "non-synchronous shrinkage effect". The rapid shrinkage of coal tar generates microscopic expansion stress on the rigid skeleton of the resin, which can effectively "spread" the carbon layer, significantly increasing the interlayer spacing (d002) of the hard carbon material. Therefore, when used in sodium-ion batteries, it can provide a more spacious thermodynamically stable storage space for sodium ions, thereby improving the capacity.

[0011] (3) The hydrolysis of silane coupling agents in water and their silanization with carbon nanotubes and carbon black can improve problems such as uneven dispersion and high interfacial impedance of carbon nanotubes and carbon black. In addition, silane coupling agents can also act as "molecular bridges" to connect conductive agents and resin matrices, preventing phase separation. At the same time, the hydrolysis products of silane coupling agents form silicon-containing nanostructures during aging or carbonization, which can be removed by alkaline washing, acid washing or water washing during the purification process. Therefore, the hydrolysis products can act as pore-forming templates and can form rich hierarchical pores in the material after purification to optimize ion transport.

[0012] As one technical solution of the present invention, the first solvent is a mixed solution of water and ethanol, and the pH is adjusted to 4-7 with acid.

[0013] As one technical solution of the present invention, the mass ratio of the carbon nanotubes to the carbon black is 0.1~1.0:1.

[0014] As one technical solution of the present invention, the mass of the carbon nanotubes and the carbon black is m1, the mass of the silane coupling agent is m2, and the ratio of m2 / m1 is 0.05~0.30:1.

[0015] As one technical solution of the present invention, the carbon nanotube is a multi-walled carbon nanotube with a diameter of 5~50nm and a length of 1~20μm.

[0016] As one technical solution of the present invention, the carbon black is conductive carbon black with a particle size of 10~50nm.

[0017] As a technical solution of the present invention, the silane coupling agent is selected from at least one of KH550, KH560, KH570, A151, A171 and A178.

[0018] As a technical solution of the present invention, the product after the silanization reaction is sequentially filtered, washed and dried to obtain the composite conductive agent.

[0019] As one technical solution of the present invention, the power of the ultrasonic treatment is 400~800W and the time is 0.5~3.0h.

[0020] As one technical solution of the present invention, the mass ratio of the phenolic resin to the coal tar is 1:0.2~1.0.

[0021] As one technical solution of the present invention, the mass of the phenolic resin and the coal tar is m3, the mass of the composite conductive agent is m4, and the m4 / m3 ratio is 0.005~0.250:1.

[0022] As one technical solution of the present invention, the coal tar is refined coal tar with a quinoline insoluble content of less than 5 wt.%.

[0023] As a technical solution of the present invention, the second solvent is selected from at least one of ethanol, acetone and isoacetone.

[0024] As one technical solution of the present invention, the heat treatment temperature is 60~100℃ and the time is 5~48h.

[0025] As one technical solution of the present invention, the aging treatment temperature is 120~200℃ and the time is 5~24h.

[0026] As a technical solution of the present invention, the first carbonization and the second carbonization are carried out under an inert atmosphere, wherein the inert atmosphere is independently selected from nitrogen, helium, neon or argon.

[0027] As one technical solution of the present invention, the temperature of the first carbonization is 300~700℃, the holding time is 2~8h, and the heating rate is 1~10℃ / min.

[0028] As a technical solution of the present invention, the first precursor is subjected to coarse crushing and then undergoes the first carbonization. The equipment used for coarse crushing is a jaw crusher, an impact crusher, or a cone crusher.

[0029] As one technical solution of the present invention, the Dv50 of the grinding material is 3~7μm.

[0030] As one technical solution of the present invention, the ash content of the second precursor is ≤0.5%.

[0031] As one technical solution of the present invention, the temperature of the second carbonization is 1000~1500℃, the holding time is 2~10h, and the heating rate is 1~10℃ / min.

[0032] As a technical solution of the present invention, after the second carbonization, the material is cooled to room temperature and then sieved, and the sieving is performed using a 200-500 mesh screen.

[0033] As a technical solution of the present invention, both the carbon nanotubes and the carbon black are subjected to oxidation treatment before the ultrasonic treatment to introduce hydroxyl and carboxyl groups on their surfaces.

[0034] As a technical solution of the present invention, the purification includes sequential alkaline washing, first water washing, acid washing, second water washing, and drying.

[0035] As one technical solution of the present invention, the alkaline washing uses a NaOH or KOH solution with a concentration of 10~50wt.%, and is stirred at 70~100℃ for 1~5h. The mass ratio of the alkaline washing solution to the grinding powder is 1~5:1.

[0036] As a technical solution of the present invention, the pickling is carried out using an aqueous solution of HF and stirred at room temperature for 1 to 24 hours, and the mass ratio of HF, grinding powder and water in the pickling is 1:1 to 5:2 to 10.

[0037] As a technical solution of the present invention, both the first water wash and the second water wash are rinsed until neutral.

[0038] As one technical solution of the present invention, the drying temperature is 45~85℃ and the time is 1~5h.

[0039] The second aspect of the present invention provides a composite hard carbon material prepared by the aforementioned method for preparing composite hard carbon material, wherein the carbon interlayer spacing d002 is 0.39~0.42 nm.

[0040] As one technical solution of the present invention, the electrical conductivity of the composite hard carbon material is 80~200S / m.

[0041] As a technical solution of the present invention, the composite hard carbon material has a three-level pore structure consisting of micropores of 0.8~1.2nm, mesopores of 10~20nm and macropores of 25~50nm, wherein the proportion of micropores is 15~25%, the proportion of mesopores is 40~50%, and the proportion of macropores is 25~35%.

[0042] As one technical solution of the present invention, the specific surface area of ​​the composite hard carbon material is 3.5~6.5m². 2 / g.

[0043] As a technical solution of the present invention, the first coulombic efficiency of the composite hard carbon material at 0.1C is ≥93.0%.

[0044] As a technical solution of the present invention, the 0.1C first reversible specific capacity of the composite hard carbon material is ≥450mAh / g.

[0045] As one technical solution of the present invention, the 1.0C rate capacity ratio of the composite hard carbon material is ≥85.0%.

[0046] A third aspect of the present invention provides a sodium-ion battery, comprising a positive electrode material, a negative electrode material and an electrolyte, wherein the negative electrode material comprises the aforementioned composite hard carbon material. Detailed Implementation

[0047] The composite hard carbon material of this invention can be used alone or in combination with other negative electrode active materials (such as natural graphite, artificial graphite, silicon oxide materials, silicon carbon materials, soft carbon, etc.). The composite hard carbon material can be applied in sodium-ion batteries, which include a positive electrode material, a separator, an electrolyte, and a negative electrode material. The positive electrode material includes layered oxide series sodium-ion positive electrode materials, Prussian blue (white) series sodium-ion positive electrode materials, and polyanionic compound series sodium-ion positive electrode materials. The separator can be a polyethylene or polypropylene separator. The electrolyte may include sodium salts, non-aqueous organic solvents, and conventional additives. The sodium salt can be selected from at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalate-borate), sodium difluorophosphate, sodium bis(oxalate-borate), sodium difluorooxalate-borate, sodium lower aliphatic carboxylic acid sodium salt, sodium difluorobis(oxalate-phosphate), sodium bis(oxalate-imide), sodium chloroborane, and sodium tetraphenylborate. The non-aqueous organic solvent is selected from at least one of γ-butyrolactone, γ-valerolactone, δ-valerolactone, methyl acetate, ethyl acetate, ethyl propionate, butyl acetate, propyl propionate, butyl propionate, ethylene carbonate, propylene carbonate, butyl carbonate, methyl pentyl carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, propylene carbonate, 1,3-dioxane, 1,4-dioxane, crown ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2-trifluoromethyltetrahydrofuran, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. The additive may be at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfite, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, and vinyl sulfate.

[0048] The composite hard carbon material of this invention exhibits an initial coulombic efficiency of ≥93.0% at 0.1C, and examples, but not limited to, 93.0%, 93.5%, 94.0%, 94.5%, 95.0%, 95.5%, 96.0%, 96.5%, and 97.0%. The initial reversible specific capacity at 0.1C is ≥450mAh / g, and examples, but not limited to, 450mAh / g, 455mAh / g, 460mAh / g, 465mAh / g, 470mAh / g, 475mAh / g, and 480mAh / g. The 1.0C rate capability is ≥85.0%, and examples, but not limited to, 85.0%, 85.5%, 86.0%, 86.5%, 87.0%, 87.5%, 88.0%, 88.5%, 89.0%, 89.5%, and 89.0%.

[0049] The carbon interlayer spacing d002 of the composite hard carbon material of the present invention is 0.39~0.42 nm. Examples, but not limited to, 0.39 nm, 0.40 nm, 0.41 nm, and 0.42 nm, are significantly higher than the traditional 0.37~0.39 nm, thus improving the storage sites and insertion / extraction kinetics of sodium ions. The electrical conductivity of the composite hard carbon material is 80~200 S / m. Examples, but not limited to, are 80 S / m, 90 S / m, 100 S / m, 110 S / m, 120 S / m, 130 S / m, 140 S / m, 150 S / m, 160 S / m, 170 S / m, 180 S / m, 190 S / m, and 200 S / m. The composite hard carbon material comprises a three-level pore structure consisting of micropores, mesopores, and macropores. The micropores have a pore size of 0.8–1.2 nm and a volume fraction of 15–25%. The mesopores have a pore size of 10–20 nm and a volume fraction of 40–50%. The macropores have a pore size of 20–50 nm and a volume fraction of 25–35%. The specific surface area is 3.5–6.5 μm². 2 / g, as an example, the specific surface area can be, but is not limited to, 3.5m². 2 / g, 3.7m 2 / g, 3.9m 2 / g, 4.1m 2 / g, 4.5m 2 / g, 4.8m 2 / g, 5.2m 2 / g, 5.5m 2 / g, 5.8m 2 / g, 6.2m 2 / g, 6.5m 2 / g.

[0050] The preparation method of the composite hard carbon material of the present invention may include the following steps: (I) preparation of composite conductive agent, (II) preparation of first precursor, (III) preparation of second precursor and (IV) high temperature carbonization.

[0051] Step (I) Preparation of the composite conductive agent includes adding carbon nanotubes and carbon black to a first solvent containing water for ultrasonic treatment, followed by adding a silane coupling agent to carry out a silanization reaction.

[0052] The carbon nanotubes are multi-walled carbon nanotubes with a diameter of 5-50 nm and a length of 1-20 μm. The carbon black is conductive carbon black with a particle size of 10-50 nm. The mass ratio of carbon nanotubes to carbon black is 0.1-1.0:1, and examples, but not limited to, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, and 1.0:1. The first solvent is a mixture of water and ethanol, and the pH is adjusted to 4-7 with an acid, such as an organic acid, acetic acid, oxalic acid, or citric acid. Both the carbon nanotubes and carbon black are oxidized before ultrasonic treatment to introduce hydroxyl and carboxyl groups onto their surfaces. Oxidation methods include heating oxidation in air, oxidation with hydrogen peroxide solution, and oxidation with nitric acid. The ultrasonic treatment power is 400~800W, and the time is 0.5~3.0h. For example, the power can be, but is not limited to, 400W, 450W, 500W, 550W, 600W, 650W, 700W, 750W, and 800W. The silane coupling agent is selected from at least one of KH550, KH560, KH570, A151, A171, and A178. The mass of carbon nanotubes and carbon black is m1, and the mass of the silane coupling agent is m2. The ratio of m2 / m1 is 0.05~0.30:1. For example, m2 / m1 can be, but is not limited to, 0.05:1, 0.10:1, 0.15:1, 0.20:1, 0.25:1, and 0.30:1. The silane coupling agent is gradually added dropwise under stirring at a speed of 200-800 rpm for 0.5-3.0 h. After the silanization reaction, the product is sequentially filtered, washed, and dried to obtain the composite conductive agent. Washing can be done with water until neutral. The drying temperature can be 35-50℃, and examples include, but are not limited to, 35℃, 37℃, 39℃, 40℃, 42℃, 44℃, 46℃, 48℃, and 50℃. The drying time can be 2-10 h, and examples include, but are not limited to, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, and 10 h.

[0053] Step (II) Preparation of the first precursor includes dissolving phenolic resin and coal tar in a second solvent, adding a composite conductive agent for dispersion, and then performing heat treatment and aging treatment.

[0054] The coal tar is refined coal tar with a quinoline insoluble content of less than 5 wt.%. The mass ratio of phenolic resin to coal tar is 1:0.2 to 1.0. For example, the mass ratio may be, but is not limited to, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, or 1:1.0. The mass of phenolic resin and coal tar is m3, and the mass of the composite conductive agent is m4. The m4 / m3 ratio is 0.005 to 0.250:1. For example, the m4 / m3 ratio may be, but is not limited to, 0.005:1, 0.010:1, 0.025:1, 0.050:1, 0.075:1, 0.100:1, 0.150:1, 0.200:1, or 0.250:1. The second solvent is selected from at least one of ethanol, acetone, and isoacetone. The heat treatment temperature is 60~100℃ and the time is 5~48h. For example, the temperature may be, but is not limited to, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, or 100℃, and the time may be, but is not limited to, 5h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 44h, or 48h. The aging treatment temperature is 120~200℃ and the time is 5~24h. For example, the temperature can be, but is not limited to, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, and the time can be, but is not limited to, 5h, 7h, 9h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h.

[0055] Step (III) The preparation of the second precursor includes the first carbonization of the first precursor followed by crushing to obtain a powder, and then purifying the powder.

[0056] The first precursor undergoes coarse crushing followed by a first carbonization. The coarse crushing equipment used is a jaw crusher, impact crusher, or cone crusher. The first carbonization is carried out under an inert atmosphere, independently selected from nitrogen, helium, neon, or argon. The temperature of the first carbonization is 300–700℃, the holding time is 2–8 hours, and the heating rate is 1–10℃ / min. For example, the temperature of the first carbonization can be, but is not limited to, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, or 700℃; the holding time can be, but is not limited to, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours; and the heating rate can be, but is not limited to, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min. Under these conditions of initial carbonization, the gradual decomposition and shrinkage of coal tar components are facilitated, resulting in a more uniform and controllable layer-expansion effect. Crushing is performed using air jet milling, and the resulting powder has a Dv50 of 3-7 μm. For example, Dv50 can be, but is not limited to, 3 μm, 4 μm, 5 μm, 6 μm, or 7 μm. Purification includes at least one of alkali washing, acid washing, and water washing. As a technical solution, purification includes sequential alkali washing, a first water wash, acid washing, a second water wash, and drying. Alkali washing uses a 10-50 wt.% NaOH or KOH solution and is stirred at 70-100°C for 1-5 hours. The mass ratio of the alkali washing solution to the powder is 1-5:1. Acid washing uses an aqueous HF solution and is stirred at room temperature for 1-24 hours. The mass ratio of HF, powder, and water in the acid washing is 1:1-5:2-10. Both the first and second water washes are performed until neutral. The drying temperature is 45~85℃, and the time is 1~5h. Impurities are removed by alkali washing, acid washing, and water washing, so the ash content of the second precursor after purification is ≤0.5%.

[0057] Step (IV) High-temperature carbonization includes a second carbonization of the second precursor.

[0058] The second carbonization is carried out under an inert atmosphere, which is independently selected from nitrogen, helium, neon, or argon. The temperature of the second carbonization is higher than that of the first carbonization, ranging from 1000 to 1500°C, with a holding time of 2 to 10 hours and a heating rate of 1 to 10°C / min. As an example, the temperature for the second carbonization can be, but is not limited to, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, or 1500℃; the holding time can be, but is not limited to, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h; and the heating rate can be, but is not limited to, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min. After the second carbonization, the material is cooled to room temperature and sieved using a 200-500 mesh screen.

[0059] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting the invention. The embodiments of this invention include descriptions of the technical solution for composite hard carbon materials and descriptions of the technical solution for the preparation method of composite hard carbon materials.

[0060] Example 1 This embodiment describes a method for preparing a composite hard carbon material, which includes the following steps.

[0061] (I) Preparation of composite conductive agent 80g of anhydrous ethanol and 10g of water were mixed, and the pH was adjusted to 4.5 with acetic acid to obtain a mixed solvent. 50g of oxidized multi-walled carbon nanotubes (CNTs, 15nm in diameter and 10μm in length) and 100g of oxidized conductive carbon black (CB, 20nm in particle size) were added to the mixed solvent and sonicated at 600W for 1h. While stirring at 400rpm, 15g of KH550 silane coupling agent was added dropwise. After the addition was complete, the reaction was allowed to proceed for 1.5h, followed by filtration, washing with water, and drying at 60℃ to obtain the composite conductive agent. The multi-walled carbon nanotubes (CNTs) and conductive carbon black (CB) were oxidized using a 30wt.% concentrated hydrogen peroxide solution.

[0062] (II) Preparation of the first precursor 1 kg of phenolic resin and 0.5 kg of refined coal tar (with a quinoline insoluble content of 4.5 wt.%) were dissolved in 0.5 kg of ethanol and stirred until homogeneous. 150 g of composite conductive agent was added and stirred for 1 hour to disperse the mixture evenly. The mixture was then cured at 95 °C for 12 hours and aged at 180 °C for 5 hours to obtain the first precursor.

[0063] (III) Preparation of the second precursor The first precursor was coarsely crushed to a particle size of approximately 12 mm using a crusher. It was then heated to 400°C at a rate of 3°C / min under a nitrogen atmosphere and held for 6 hours. After cooling, it was pulverized using an air jet mill to obtain a powder with a Dv50 of 5 μm. For every 1 kg of the powder, it was soaked and stirred in a 2 kg 20 wt.% NaOH aqueous solution at 95°C for 3 hours, then washed with water until neutral. Next, it was soaked and stirred in a mixture of 0.4 kg HF and 2 kg water at room temperature for 12 hours, then washed with water until neutral. Finally, it was dried at 60°C for 3 hours to obtain a second precursor with an ash content of 0.35%.

[0064] (IV) High temperature carbonization The second precursor was heated to 1300℃ at a rate of 6℃ / min under a nitrogen atmosphere and held at that temperature for 4 hours. After cooling to room temperature, it was passed through a 325-mesh sieve to obtain the composite hard carbon material.

[0065] Example 2 This embodiment describes a method for preparing a composite hard carbon material, which includes the following steps.

[0066] (I) Preparation of composite conductive agent 80g of anhydrous ethanol and 10g of water were mixed, and the pH was adjusted to 4.5 with acetic acid to obtain a mixed solvent. 50g of oxidized multi-walled carbon nanotubes (CNTs, 15nm in diameter and 10μm in length) and 100g of oxidized conductive carbon black (CB, 20nm in particle size) were added to the mixed solvent and sonicated at 600W for 1h. While stirring at 400rpm, 15g of KH550 silane coupling agent was added dropwise. After the addition was complete, the reaction was allowed to proceed for 1.5h, followed by filtration, washing with water, and drying at 60℃ to obtain the composite conductive agent. The multi-walled carbon nanotubes (CNTs) and conductive carbon black (CB) were oxidized using a 30wt.% concentrated hydrogen peroxide solution.

[0067] (II) Preparation of the first precursor 1 kg of phenolic resin and 1.0 kg of refined coal tar (with a quinoline insoluble content of 4.5 wt.%) were dissolved in 0.5 kg of ethanol and stirred until homogeneous. 150 g of composite conductive agent was added and stirred for 1 hour to disperse the mixture evenly. The mixture was then cured at 95 °C for 12 hours and aged at 180 °C for 5 hours to obtain the first precursor.

[0068] (III) Preparation of the second precursor The first precursor was coarsely crushed to a particle size of approximately 12 mm using a crusher. It was then heated to 400°C at a rate of 3°C / min under a nitrogen atmosphere and held for 6 hours. After cooling, it was pulverized using an air jet mill to obtain a powder with a Dv50 of 5 μm. For every 1 kg of the powder, it was soaked and stirred in a 2 kg 20 wt.% NaOH aqueous solution at 95°C for 3 hours, then washed with water until neutral. Next, it was soaked and stirred in a mixture of 0.4 kg HF and 2 kg water at room temperature for 12 hours, then washed with water until neutral. Finally, it was dried at 60°C for 3 hours to obtain a second precursor with an ash content of 0.35%.

[0069] (IV) High temperature carbonization The second precursor was heated to 1300℃ at a rate of 6℃ / min under a nitrogen atmosphere and held at that temperature for 4 hours. After cooling to room temperature, it was passed through a 325-mesh sieve to obtain the composite hard carbon material.

[0070] Example 3 This embodiment describes a method for preparing a composite hard carbon material, which includes the following steps.

[0071] (I) Preparation of composite conductive agent 80g of anhydrous ethanol and 10g of water were mixed, and the pH was adjusted to 4.5 with acetic acid to obtain a mixed solvent. 50g of oxidized multi-walled carbon nanotubes (CNTs, 15nm in diameter and 10μm in length) and 100g of oxidized conductive carbon black (CB, 20nm in particle size) were added to the mixed solvent and sonicated at 600W for 1h. While stirring at 400rpm, 15g of KH550 silane coupling agent was added dropwise. After the addition was complete, the reaction was allowed to proceed for 1.5h, followed by filtration, washing with water, and drying at 60℃ to obtain the composite conductive agent. The multi-walled carbon nanotubes (CNTs) and conductive carbon black (CB) were oxidized using a 30wt.% concentrated hydrogen peroxide solution.

[0072] (II) Preparation of the first precursor Dissolve 1 kg of phenolic resin and 0.2 kg of refined coal tar (with a quinoline insoluble content of 4.5 wt.%) in 0.5 kg of ethanol and stir until homogeneous. Add 150 g of composite conductive agent and continue stirring for 1 hour to disperse evenly. Then cure at 95 °C for 12 hours and age at 180 °C for 5 hours to obtain the first precursor.

[0073] (III) Preparation of the second precursor The first precursor was coarsely crushed to a particle size of approximately 12 mm using a crusher. It was then heated to 400°C at a rate of 3°C / min under a nitrogen atmosphere and held for 6 hours. After cooling, it was pulverized using an air jet mill to obtain a powder with a Dv50 of 5 μm. For every 1 kg of the powder, it was soaked and stirred in a 2 kg 20 wt.% NaOH aqueous solution at 95°C for 3 hours, then washed with water until neutral. Next, it was soaked and stirred in a mixture of 0.4 kg HF and 2 kg water at room temperature for 12 hours, then washed with water until neutral. Finally, it was dried at 60°C for 3 hours to obtain a second precursor with an ash content of 0.35%.

[0074] (IV) High temperature carbonization The second precursor was heated to 1300℃ at a rate of 6℃ / min under a nitrogen atmosphere and held at that temperature for 4 hours. After cooling to room temperature, it was passed through a 325-mesh sieve to obtain the composite hard carbon material.

[0075] Example 4 This embodiment describes a method for preparing a composite hard carbon material, which includes the following steps.

[0076] (I) Preparation of composite conductive agent 80g of anhydrous ethanol and 20g of water were mixed, and the pH was adjusted to 5.0 with oxalic acid to obtain a mixed solvent. 70g of oxidized multi-walled carbon nanotubes (CNTs, 15nm in diameter and 10μm in length) and 100g of oxidized conductive carbon black (CB, 20nm in particle size) were added to the mixed solvent and sonicated at 750W for 0.5h. While stirring at 400rpm, 15g of A171 silane coupling agent was added dropwise. After the addition was complete, the reaction was carried out for 1.5h, then filtered, washed with water, and dried at 60℃ to obtain a composite conductive agent. Multi-walled carbon nanotubes (CNTs) and conductive carbon black (CB) were then subjected to heating oxidation treatment in air.

[0077] (II) Preparation of the first precursor 1 kg of phenolic resin and 0.5 kg of refined coal tar (with a quinoline insoluble content of 4.8 wt.%) were dissolved in 1.0 kg of acetone and stirred until homogeneous. 135 g of composite conductive agent was added and stirred for 1 hour to disperse the mixture evenly. The mixture was then cured at 95 °C for 12 hours and aged at 200 °C for 10 hours to obtain the first precursor.

[0078] (III) Preparation of the second precursor The first precursor was coarsely crushed to a particle size of approximately 12 mm using a crusher. It was then heated to 550°C at a rate of 5°C / min under a helium atmosphere and held for 4 hours. After cooling, it was pulverized using an air jet mill to obtain a powder with a Dv50 of 5 μm. For each kg of powder, 2 kg of a 20 wt.% NaOH aqueous solution was soaked and stirred at 95°C for 3 hours, then washed with water until neutral. Next, a mixture of 0.4 kg HF and 2 kg water was soaked and stirred at room temperature for 12 hours, then washed with water until neutral. Finally, it was dried at 75°C for 2 hours to obtain a second precursor with an ash content of 0.40%.

[0079] (IV) High temperature carbonization The second precursor was heated to 1150°C at a rate of 6°C / min under a nitrogen atmosphere and held at that temperature for 6 hours. After cooling to room temperature, it was passed through a 325-mesh sieve to obtain the composite hard carbon material.

[0080] Example 5 This embodiment describes a method for preparing a composite hard carbon material, which includes the following steps.

[0081] (I) Preparation of composite conductive agent 80g of anhydrous ethanol and 10g of water were mixed, and the pH was adjusted to 4.5 with acetic acid to obtain a mixed solvent. 50g of oxidized multi-walled carbon nanotubes (CNTs, 40nm in diameter and 15μm in length) and 100g of oxidized conductive carbon black (CB, 35nm in particle size) were added to the mixed solvent, and the mixture was sonicated at 600W for 1h. While stirring at 400rpm, 30g of KH550 silane coupling agent was added dropwise. After the addition was complete, the reaction was carried out for 1.5h, then filtered, washed with water, and dried at 60℃ to obtain the composite conductive agent. The multi-walled carbon nanotubes (CNTs) and conductive carbon black (CB) were oxidized using 40wt.% nitric acid.

[0082] (II) Preparation of the first precursor 1 kg of phenolic resin and 0.7 kg of refined coal tar (with a quinoline insoluble content of 4.5 wt.%) were dissolved in 0.5 kg of ethanol and stirred until homogeneous. 150 g of composite conductive agent was added and stirred for 1 hour to disperse the mixture evenly. The mixture was then cured at 80 °C for 20 hours and aged at 150 °C for 10 hours to obtain the first precursor.

[0083] (III) Preparation of the second precursor The first precursor was coarsely crushed to a particle size of approximately 10 mm using an impact crusher. It was then heated to 400°C at a rate of 5°C / min under a nitrogen atmosphere and held for 6 hours. After cooling, it was pulverized using an air jet mill to obtain a powder with a Dv50 of 4 μm. For every 1 kg of the powder, it was soaked and stirred in 3.5 kg of a 35 wt.% KOH aqueous solution at 85°C for 4 hours, then washed with water until neutral, and dried at 60°C for 3 hours to obtain a second precursor with an ash content of 0.35%.

[0084] (IV) High temperature carbonization The second precursor was heated to 1300℃ at a rate of 4℃ / min under a nitrogen atmosphere and held at that temperature for 4h. After cooling to room temperature, it was passed through a 375-mesh sieve to obtain the composite hard carbon material.

[0085] Example 6 This embodiment describes a method for preparing a composite hard carbon material, which includes the following steps.

[0086] (I) Preparation of composite conductive agent 80g of anhydrous ethanol and 30g of water were mixed, and the pH was adjusted to 5.5 with acetic acid to obtain a mixed solvent. 50g of oxidized multi-walled carbon nanotubes (CNTs, 15nm in diameter and 10μm in length) and 100g of oxidized conductive carbon black (CB, 20nm in particle size) were added to the mixed solvent and sonicated at 750W for 0.5h. While stirring at 550rpm, 20g of KH560 silane coupling agent was added dropwise. After the addition was complete, the reaction was carried out for 2.0h, then filtered, washed with water, and dried at 70℃ to obtain the composite conductive agent. The multi-walled carbon nanotubes (CNTs) and conductive carbon black (CB) were oxidized using a 30wt.% concentrated hydrogen peroxide solution.

[0087] (II) Preparation of the first precursor 1 kg of phenolic resin and 0.7 kg of refined coal tar (with a quinoline insoluble content of 4.0 wt.%) were dissolved in 0.5 kg of ethanol and stirred until homogeneous. 150 g of composite conductive agent was added and stirred for 2 hours to disperse the mixture evenly. The mixture was then cured at 90 °C for 15 hours and aged at 150 °C for 15 hours to obtain the first precursor.

[0088] (III) Preparation of the second precursor The first precursor was coarsely crushed to a particle size of approximately 12 mm using a crusher. It was then heated to 400°C at a rate of 3°C / min under a nitrogen atmosphere and held for 6 hours. After cooling, it was pulverized using an air jet mill to produce a powder with a Dv50 of 5 μm. For each kg of the powder, it was soaked and stirred in a 6 kg 10 wt.% NaOH aqueous solution at 100°C for 6 hours, then washed with water until neutral. Next, it was soaked and stirred in a mixture of 0.5 kg HF and 3.5 kg water at room temperature for 16 hours, washed again until neutral, and dried at 75°C for 2 hours to obtain a second precursor with an ash content of 0.35%.

[0089] (IV) High temperature carbonization The second precursor was heated to 1000℃ at a rate of 8℃ / min under a nitrogen atmosphere and held at that temperature for 6 hours. After cooling to room temperature, it was passed through a 325-mesh sieve to obtain the composite hard carbon material.

[0090] Comparative Example 1 This comparative example illustrates a method for preparing a composite hard carbon material, comprising the following steps.

[0091] (I) Preparation of composite conductive agent 80g of anhydrous ethanol and 10g of water were mixed, and the pH was adjusted to 4.5 with acetic acid to obtain a mixed solvent. 50g of oxidized multi-walled carbon nanotubes (CNTs, 15nm in diameter and 10μm in length) and 100g of oxidized conductive carbon black (CB, 20nm in particle size) were added to the mixed solvent and sonicated at 600W for 1h. While stirring at 400rpm, 15g of KH550 silane coupling agent was added dropwise. After the addition was complete, the reaction was allowed to proceed for 1.5h, followed by filtration, washing with water, and drying at 60℃ to obtain the composite conductive agent. The multi-walled carbon nanotubes (CNTs) and conductive carbon black (CB) were oxidized using a 30wt.% concentrated hydrogen peroxide solution.

[0092] (II) Preparation of the first precursor Dissolve 1.5 kg of phenolic resin in 0.5 kg of ethanol and stir until homogeneous. Add 150 g of composite conductive agent and continue stirring for 1 hour to disperse evenly. Then cure at 95 °C for 12 hours and age at 180 °C for 5 hours to obtain the first precursor.

[0093] (III) Preparation of the second precursor The first precursor was coarsely crushed to a particle size of approximately 12 mm using a crusher. It was then heated to 400°C at a rate of 3°C / min under a nitrogen atmosphere and held for 6 hours. After cooling, it was pulverized using an air jet mill to obtain a powder with a Dv50 of 5 μm. For every 1 kg of the powder, it was soaked and stirred in a 2 kg 20 wt.% NaOH aqueous solution at 95°C for 3 hours, then washed with water until neutral. Next, it was soaked and stirred in a mixture of 0.4 kg HF and 2 kg water at room temperature for 12 hours, then washed with water until neutral. Finally, it was dried at 60°C for 3 hours to obtain a second precursor with an ash content of 0.35%.

[0094] (IV) High temperature carbonization The second precursor was heated to 1300℃ at a rate of 6℃ / min under a nitrogen atmosphere and held at that temperature for 4 hours. After cooling to room temperature, it was passed through a 325-mesh sieve to obtain the composite hard carbon material.

[0095] Comparative Example 2 This comparative example illustrates a method for preparing a composite hard carbon material, comprising the following steps.

[0096] (I) Preparation of composite conductive agent 80g of anhydrous ethanol and 10g of water were mixed, and the pH was adjusted to 4.5 with acetic acid to obtain a mixed solvent. 50g of oxidized multi-walled carbon nanotubes (CNTs, 15nm in diameter and 10μm in length) and 100g of oxidized conductive carbon black (CB, 20nm in particle size) were added to the mixed solvent and sonicated at 600W for 1h. While stirring at 400rpm, 15g of KH550 silane coupling agent was added dropwise. After the addition was complete, the reaction was allowed to proceed for 1.5h, followed by filtration, washing with water, and drying at 60℃ to obtain the composite conductive agent. The multi-walled carbon nanotubes (CNTs) and conductive carbon black (CB) were oxidized using a 30wt.% concentrated hydrogen peroxide solution.

[0097] (II) Preparation of the first precursor 1.5 kg of refined coal tar (with a quinoline insoluble content of 4.5 wt.%) was dissolved in 0.5 kg of ethanol and stirred until homogeneous. 150 g of composite conductive agent was added and stirred for 1 hour to disperse the mixture evenly. The mixture was then cured at 95 °C for 12 hours and aged at 180 °C for 5 hours to obtain the first precursor.

[0098] (III) Preparation of the second precursor The first precursor was coarsely crushed to a particle size of approximately 12 mm using a crusher. It was then heated to 400°C at a rate of 3°C / min under a nitrogen atmosphere and held for 6 hours. After cooling, it was pulverized using an air jet mill to obtain a powder with a Dv50 of 5 μm. For every 1 kg of the powder, it was soaked and stirred in a 2 kg 20 wt.% NaOH aqueous solution at 95°C for 3 hours, then washed with water until neutral. Next, it was soaked and stirred in a mixture of 0.4 kg HF and 2 kg water at room temperature for 12 hours, then washed with water until neutral. Finally, it was dried at 60°C for 3 hours to obtain a second precursor with an ash content of 0.35%.

[0099] (IV) High temperature carbonization The second precursor was heated to 1300℃ at a rate of 6℃ / min under a nitrogen atmosphere and held at that temperature for 4 hours. After cooling to room temperature, it was passed through a 325-mesh sieve to obtain the composite hard carbon material.

[0100] Comparative Example 3 This comparative example illustrates a method for preparing a composite hard carbon material, comprising the following steps.

[0101] (I) Preparation of composite conductive agent 80g of anhydrous ethanol and 10g of water were mixed, and the pH was adjusted to 4.5 with acetic acid to obtain a mixed solvent. 50g of oxidized multi-walled carbon nanotubes (CNTs, 15nm in diameter and 10μm in length) and 100g of oxidized conductive carbon black (CB, 20nm in particle size) were added to the mixed solvent and sonicated at 600W for 1 hour. The mixture was then filtered, washed with water, and dried at 60℃ to obtain a composite conductive agent. The multi-walled carbon nanotubes (CNTs) and conductive carbon black (CB) were oxidized using a 30wt.% concentrated hydrogen peroxide solution.

[0102] (II) Preparation of the first precursor 1 kg of phenolic resin and 0.5 kg of refined coal tar (with a quinoline insoluble content of 4.5 wt.%) were dissolved in 0.5 kg of ethanol and stirred until homogeneous. 150 g of composite conductive agent was added and stirred for 1 hour to disperse the mixture evenly. The mixture was then cured at 95 °C for 12 hours and aged at 180 °C for 5 hours to obtain the first precursor.

[0103] (III) Preparation of the second precursor The first precursor was coarsely crushed to a particle size of approximately 12 mm using a crusher. It was then heated to 400°C at a rate of 3°C / min under a nitrogen atmosphere and held for 6 hours. After cooling, it was pulverized using an air jet mill to obtain a powder with a Dv50 of 5 μm. For every 1 kg of the powder, it was soaked and stirred in a 2 kg 20 wt.% NaOH aqueous solution at 95°C for 3 hours, then washed with water until neutral. Next, it was soaked and stirred in a mixture of 0.4 kg HF and 2 kg water at room temperature for 12 hours, then washed with water until neutral. Finally, it was dried at 60°C for 3 hours to obtain a second precursor with an ash content of 0.35%.

[0104] (IV) High temperature carbonization The second precursor was heated to 1300℃ at a rate of 6℃ / min under a nitrogen atmosphere and held at that temperature for 4 hours. After cooling to room temperature, it was passed through a 325-mesh sieve to obtain the composite hard carbon material.

[0105] Comparative Example 4 This comparative example illustrates a method for preparing a composite hard carbon material, comprising the following steps.

[0106] (I) Preparation of composite conductive agent 80g of anhydrous ethanol and 10g of water were mixed, and the pH was adjusted to 4.5 with acetic acid to obtain a mixed solvent. 150g of oxidized multi-walled carbon nanotubes (CNTs, 15nm in diameter and 10μm in length) were added to the mixed solvent, and the mixture was sonicated at 600W for 1h. While stirring at 400rpm, 15g of KH550 silane coupling agent was added dropwise. After the addition was complete, the reaction was carried out for 1.5h, then filtered, washed with water, and dried at 60℃ to obtain the composite conductive agent. Multi-walled carbon nanotubes (CNTs) and conductive carbon black (CB) were oxidized using a 30wt.% concentrated hydrogen peroxide solution.

[0107] (II) Preparation of the first precursor 1 kg of phenolic resin and 0.5 kg of refined coal tar (with a quinoline insoluble content of 4.5 wt.%) were dissolved in 0.5 kg of ethanol and stirred until homogeneous. 150 g of composite conductive agent was added and stirred for 1 hour to disperse the mixture evenly. The mixture was then cured at 95 °C for 12 hours and aged at 180 °C for 5 hours to obtain the first precursor.

[0108] (III) Preparation of the second precursor The first precursor was coarsely crushed to a particle size of approximately 12 mm using a crusher. It was then heated to 400°C at a rate of 3°C / min under a nitrogen atmosphere and held for 6 hours. After cooling, it was pulverized using an air jet mill to obtain a powder with a Dv50 of 5 μm. For every 1 kg of the powder, it was soaked and stirred in a 2 kg 20 wt.% NaOH aqueous solution at 95°C for 3 hours, then washed with water until neutral. Next, it was soaked and stirred in a mixture of 0.4 kg HF and 2 kg water at room temperature for 12 hours, then washed with water until neutral. Finally, it was dried at 60°C for 3 hours to obtain a second precursor with an ash content of 0.35%.

[0109] (IV) High temperature carbonization The second precursor was heated to 1300℃ at a rate of 6℃ / min under a nitrogen atmosphere and held at that temperature for 4 hours. After cooling to room temperature, it was passed through a 325-mesh sieve to obtain the composite hard carbon material.

[0110] Comparative Example 5 This comparative example illustrates a method for preparing a composite hard carbon material, comprising the following steps.

[0111] (I) Preparation of composite conductive agent 80g of anhydrous ethanol and 10g of water were mixed, and the pH was adjusted to 4.5 with acetic acid to obtain a mixed solvent. 150g of oxidized conductive carbon black (CB, particle size 20nm) was added to the mixed solvent, and the mixture was sonicated at 600W for 1h. While stirring at 400rpm, 15g of KH550 silane coupling agent was added dropwise. After the addition was complete, the reaction was carried out for 1.5h, then filtered, washed with water, and dried at 60℃ to obtain the composite conductive agent. Multi-walled carbon nanotubes (CNTs) and conductive carbon black (CB) were oxidized using a 30wt.% concentrated hydrogen peroxide solution.

[0112] (II) Preparation of the first precursor 1 kg of phenolic resin and 0.5 kg of refined coal tar (with a quinoline insoluble content of 4.5 wt.%) were dissolved in 0.5 kg of ethanol and stirred until homogeneous. 150 g of composite conductive agent was added and stirred for 1 hour to disperse the mixture evenly. The mixture was then cured at 95 °C for 12 hours and aged at 180 °C for 5 hours to obtain the first precursor.

[0113] (III) Preparation of the second precursor The first precursor was coarsely crushed to a particle size of approximately 12 mm using a crusher. It was then heated to 400°C at a rate of 3°C / min under a nitrogen atmosphere and held for 6 hours. After cooling, it was pulverized using an air jet mill to obtain a powder with a Dv50 of 5 μm. For every 1 kg of the powder, it was soaked and stirred in a 2 kg 20 wt.% NaOH aqueous solution at 95°C for 3 hours, then washed with water until neutral. Next, it was soaked and stirred in a mixture of 0.4 kg HF and 2 kg water at room temperature for 12 hours, then washed with water until neutral. Finally, it was dried at 60°C for 3 hours to obtain a second precursor with an ash content of 0.35%.

[0114] (IV) High temperature carbonization The second precursor was heated to 1300℃ at a rate of 6℃ / min under a nitrogen atmosphere and held at that temperature for 4 hours. After cooling to room temperature, it was passed through a 325-mesh sieve to obtain the composite hard carbon material.

[0115] The composite hard carbon materials prepared in Examples 1-6 and Comparative Examples 1-5 were tested for physical properties and chemical composition. The results are shown in Table 1. The test conditions are as follows.

[0116] The carbon interlayer spacing (d002) of the composite hard carbon material was determined using X-ray diffraction (XRD). The BET specific surface area was determined using a specific surface area and porosity analyzer. The electrical conductivity of the composite hard carbon material was tested using a conductivity meter. Pore size analysis was performed using an ASAP2460 multi-station fully automated specific surface area and pore size analyzer.

[0117] Electrochemical performance testing procedure: The composite hard carbon materials, polyvinylidene fluoride (PVDF), and conductive carbon black prepared in Examples 1-6 and Comparative Examples 1-5 were mixed at a mass ratio of 90:5:5 to form a slurry, which was then coated onto copper foil and dried before being punched. A 2430 coin cell was assembled in an argon glove box, using a sodium metal sheet as the counter electrode and 1M NaClO4, EC / DMC / EMC (1:1:1, v / v / v) as the electrolyte. After assembly, the cells were placed in a 25℃ constant temperature oven for standby. The coin cells were tested using a LAND CT 3002A charge / discharge test cabinet within a voltage range of 0-3.0V and a current density of 2A / g. The initial charge / discharge capacity and coulombic efficiency were tested at 0.1C, and the rate performance at 1.0C was also tested.

[0118] Table 1 Performance test results of composite hard carbon materials in Examples 1-6 and Comparative Examples 1-5

[0119] As shown in Table 1, the composite hard carbon materials of Examples 1-6 have better physical and electrochemical properties. This indicates that the preparation method of the present invention uses carbon nanotubes and carbon black as composite conductive agents and co-silanizes them to construct a three-dimensional conductive network. Phenolic resin and coal tar are used as carbon sources to induce asynchronous shrinkage to expand the interlayer spacing of hard carbon. Then, the hydrolysis products of silane coupling agent are used as pore-forming templates. This method can achieve triple synergistic optimization of the carbon interlayer spacing, hierarchical pores and conductive network of hard carbon. Therefore, the prepared composite hard carbon materials have better electrochemical performance.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a composite hard carbon material, characterized in that, Including the following steps: (I) Preparation of composite conductive agent Carbon nanotubes and carbon black were added to a first solvent containing water and ultrasonically treated. Then, a silane coupling agent was added to carry out a silanization reaction. (II) Preparation of the first precursor Phenolic resin and coal tar are dissolved in a second solvent, and the composite conductive agent is added and dispersed before heat treatment and aging treatment. (III) Preparation of the second precursor The first precursor is carbonized for the first time and then crushed to obtain a grinding powder. The grinding powder is purified, and the purification includes at least one of alkali washing, acid washing and water washing. (IV) High temperature carbonization The second precursor is carbonized a second time at a temperature higher than that of the first carbonization.

2. The method for preparing the composite hard carbon material according to claim 1, characterized in that, Includes at least one of the following features (1) to (22): (1) The first solvent is a mixed solution of water and ethanol, and the pH is adjusted to 4~7 with acid; (2) The mass ratio of the carbon nanotubes to the carbon black is 0.1~1.0:1; (3) The mass of the carbon nanotubes and the carbon black is m1, the mass of the silane coupling agent is m2, and the ratio of m2 to m1 is 0.05 to 0.30:1; (4) The carbon nanotubes are multi-walled carbon nanotubes with a diameter of 5~50nm and a length of 1~20μm; (5) The carbon black is conductive carbon black with a particle size of 10~50nm; (6) The silane coupling agent is selected from at least one of KH550, KH560, KH570, A151, A171 and A178; (7) After the silanization reaction, the product is filtered, washed and dried in sequence to obtain the composite conductive agent; (8) The power of the ultrasonic treatment is 400~800W, and the time is 0.5~3.0h; (9) The mass ratio of the phenolic resin to the coal tar is 1:0.2~1.0; (10) The mass of the phenolic resin and the coal tar is m3, the mass of the composite conductive agent is m4, and the m4 / m3 ratio is 0.005~0.250:1; (11) The coal tar is refined coal tar with a quinoline insoluble content of less than 5 wt.%; (12) The second solvent is selected from at least one of ethanol, acetone and isoacetone; (13) The heat treatment temperature is 60~100℃ and the time is 5~48h; (14) The aging treatment is performed at a temperature of 120~200℃ for 5~24h; (15) The first carbonization and the second carbonization are carried out under an inert atmosphere, each of which is independently selected from nitrogen, helium, neon or argon; (16) The temperature of the first carbonization is 300~700℃, the holding time is 2~8h, and the heating rate is 1~10℃ / min; (17) The first precursor is subjected to coarse crushing and then the first carbonization is carried out. The equipment used for coarse crushing is a jaw crusher, an impact crusher or a cone crusher. (18) The Dv50 of the grinding material is 3~7μm; (19) The ash content of the second precursor is ≤0.5%; (20) The temperature of the second carbonization is 1000~1500℃, the holding time is 2~10h, and the heating rate is 1~10℃ / min; (21) After the second carbonization, the material is cooled to room temperature and then sieved. The sieve is made using a 200-500 mesh screen. (22) Both the carbon nanotubes and the carbon black are oxidized before the ultrasonic treatment to introduce hydroxyl and carboxyl groups on their surfaces.

3. The method for preparing the composite hard carbon material according to claim 1, characterized in that, The purification process includes sequential alkaline washing, a first water washing, acid washing, a second water washing, and drying.

4. The method for preparing the composite hard carbon material according to claim 3, characterized in that, The alkaline washing uses a NaOH or KOH solution with a concentration of 10-50 wt.%, and is stirred at 70-100℃ for 1-5 hours. The mass ratio of the alkaline washing solution to the grinding powder is 1-5:

1.

5. The method for preparing the composite hard carbon material according to claim 3, characterized in that, The pickling process uses an aqueous solution of HF and is stirred at room temperature for 1 to 24 hours. The mass ratio of HF, grinding powder and water in the pickling process is 1:1 to 5:2 to 10.

6. The method for preparing the composite hard carbon material according to claim 3, characterized in that, Both the first and second water washes were rinsed until neutral.

7. The method for preparing the composite hard carbon material according to claim 3, characterized in that, The drying temperature is 45~85℃, and the time is 1~5h.

8. The composite hard carbon material prepared by the method for preparing composite hard carbon material according to any one of claims 1 to 7, characterized in that, The carbon interlayer spacing d002 is 0.39~0.42 nm.

9. The composite hard carbon material according to claim 8, characterized in that, Includes at least one of the following features (i) to (vi): (i) Electrical conductivity is 80~200 S / m; (ii) It has a three-level pore structure consisting of micropores of 0.8~1.2nm, mesopores of 10~20nm and macropores of 25~50nm, wherein the proportion of micropores is 15~25%, the proportion of mesopores is 40~50%, and the proportion of macropores is 25~35%; (iii) Specific surface area is 3.5~6.5m² 2 / g; (iv) Initial coulombic efficiency at 0.1C ≥ 93.0%; (v) 0.1C first reversible specific capacity ≥ 450mAh / g; (vi) 1.0C rate capacity ratio ≥ 85.0%.

10. A sodium-ion battery, comprising a positive electrode material, a negative electrode material, and an electrolyte, characterized in that, The negative electrode material includes the composite hard carbon material as described in claim 8 or 9.

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