Hard carbon material, method of preparation and use

Abstract

The application discloses a kind of hard carbon materials, preparation method and application.The carbon precursor is mixed with activating agent mixture low-temperature carbonization, and active carbon material is obtained, active carbon material adsorbs sodium ion in organic solution, and sodium-impregnated active carbon material is obtained, and after high-temperature carbonization of sodium-impregnated active carbon material, hard carbon material is obtained.The hard carbon material of the application has the advantages of less defects, rich porosity, and has the functions of sodium supplement and pre-sodium, and can effectively improve the initial coulomb efficiency of sodium ion battery in the application of sodium ion battery.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically, to hard carbon materials, preparation methods, and applications. Background Technology

[0002] Hard carbon materials are considered the most commercially promising anode material for sodium-ion batteries due to their advantages such as low cost and abundant raw materials. However, the low first-cycle coulombic efficiency (ICE) is one of the main obstacles to practical application. Effectively improving the ICE of hard carbon anodes is crucial to improving the energy density of sodium-ion full cells and is of great significance to the commercial application of sodium-ion batteries.

[0003] Pre-sodiumation is a relatively effective method to compensate for the irreversible loss of sodium ions in sodium-ion batteries. For example, RSCAdv.2015.5.106519-106522 describes obtaining pre-sodiumated Na through disassembly and recombination. x HC negative electrode, but this operation is complicated and involves disassembly and reassembly processes, making it difficult to use in actual production.

[0004] Therefore, a simplified method for preparing hard carbon materials is particularly necessary, and in view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide hard carbon materials, preparation methods, and applications, wherein the application of hard carbon materials in batteries can improve the first-cycle coulombic efficiency of the batteries.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a method for preparing a hard carbon material, comprising the following three steps: (1) The mixture of carbon precursor and activator is carbonized at low temperature to obtain activated carbon material; (2) The mixed slurry composed of the activated carbon material, sodium alkoxy and solvent is dried to obtain sodium-impregnated activated carbon material; (3) The sodium-impregnated activated carbon material is carbonized at high temperature to obtain the hard carbon material; The mass ratio of the carbon precursor to the activator is (1-6):1; The low-temperature carbonization temperature is 700-900℃; In the mixed slurry, the mass / molar ratio of the activated carbon material to the sodium alkoxy is 12:(0.03-0.5) (g / mol).

[0007] In an optional embodiment, the mass / molar ratio of the activated carbon material to the sodium alkoxy in the mixed slurry is 12:(0.05-0.2) (g / mol).

[0008] In an optional embodiment, the carbon precursor is selected from at least one of biomass-based carbon materials, resin-based carbon materials, sugar-based carbon materials, and petroleum-based carbon materials; And / or, the activator is selected from at least one of alkali metal hydroxides, acrylate polymers, inorganic oxyacids, transition metal chlorides, and trialkylamines.

[0009] In an optional embodiment, the mass concentration of activated carbon material in the mixed slurry is 5-45 g / L.

[0010] In an optional embodiment, the molar concentration of sodium alkoxy in the mixed slurry is 0.03-0.5 mol / L.

[0011] In an optional embodiment, the sodium alkoxy is a C1-C8 sodium alkoxy.

[0012] In an optional embodiment, the mass / molar ratio of the activated carbon material to the sodium alkoxy in the mixed slurry is 12:(0.08-0.15) (g / mol). And / or, the concentration of activated carbon material in the mixed slurry is 10-15 g / L; And / or, the concentration of sodium alkoxy in the mixed slurry is 0.05-0.2 mol / L; And / or, the sodium alkoxy is a C1-C4 sodium alkoxy.

[0013] In an optional embodiment, the mass / molar ratio of the activated carbon material to the sodium alkoxy in the mixed slurry is 12:0.1 (g / mol). And / or, the carbonization time of the low-temperature carbonization is 0.5-2 hours and the atmosphere is an inert atmosphere; And / or, the heating rate for the low-temperature carbonization is 0.5-3℃ / min; And / or, it also includes sequentially washing, filtering and drying the material after low-temperature carbonization to obtain activated carbon material.

[0014] In an optional embodiment, the solvent is selected from at least one of alcohol solvents, organic acid solvents, and ammonia solvents.

[0015] In an optional embodiment, the high-temperature carbonization is carried out at a carbonization temperature of 800-1400°C, for a carbonization time of 0.5-2 hours, and in an inert atmosphere. And / or, the heating rate of the high-temperature carbonization is 0.5-3℃ / min.

[0016] Secondly, the present invention provides a hard carbon material prepared by any one of the preparation methods described in the foregoing embodiments.

[0017] In an optional embodiment, the average closed-pore diameter of the hard carbon material is 1.6-3.0 nm.

[0018] In an optional embodiment, the hard carbon material A D / A G It is 1.1-1.7.

[0019] In an optional embodiment, the specific surface area of ​​the closed pores in the hard carbon material is 200-450 m². 2 g -1 .

[0020] Thirdly, the present invention provides a negative electrode sheet comprising the sodium-rich hard carbon material described in the foregoing embodiments.

[0021] Fourthly, the present invention provides a battery comprising the negative electrode sheet described in the foregoing embodiments.

[0022] The present invention has the following beneficial effects: By leveraging the strong adsorption of metallic sodium ions in sodium solution by activated carbon materials, the adsorbed metallic sodium ions exert multiple synergistic effects on hard carbon during high-temperature carbonization: on the one hand, they can catalyze graphitization, enhance the orderliness of the carbon layer, and repair surface defects; on the other hand, metallic sodium ions can also act as an in-situ pore-forming agent, constructing abundant micropores and closed pores inside the carbon matrix, adjusting the pore structure of the hard carbon material. In addition, the adsorbed sodium ions also have a certain role in sodium replenishment and pre-sodiumization. Under the multiple microscopic synergistic effects, the first-cycle coulombic efficiency (ICE) of hard carbon materials can be effectively improved. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart of the preparation of hard carbon materials in Example 1; Figure 2 This is a schematic diagram of the hard carbon material prepared in Example 1. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0026] This invention provides a method for preparing hard carbon materials, the process of which is as follows: Figure 1 As shown, it includes the following three steps: (1) The mixture of carbon precursor and activator is carbonized at low temperature to obtain activated carbon material; (2) The mixed slurry composed of the activated carbon material, sodium alkoxy and solvent is dried to obtain sodium-impregnated activated carbon material; (3) The sodium-impregnated activated carbon material is carbonized at high temperature to obtain the hard carbon material; The mass ratio of the carbon precursor to the activator is (1-6):1; The low-temperature carbonization temperature is 700-900℃; In the mixed slurry, the mass / molar ratio of the activated carbon material to the sodium alkoxy is 12:(0.03-0.5) (g / mol).

[0027] This invention mixes a carbon precursor with an activator and performs low-temperature carbonization to form a highly adsorbent activated carbon material. The activated carbon material then efficiently adsorbs sodium ions from the mixed slurry. After the solvent evaporates, a sodium-impregnated activated carbon material is formed. This sodium-impregnated activated carbon material is then carbonized at high temperature to obtain a high-efficiency hard carbon material. The activated carbon material exhibits strong adsorption of sodium ions from organic sodium salts. During high-temperature carbonization, the adsorbed sodium has multiple synergistic effects: ① it can catalyze graphitization, improving the ordering of the carbon layer and repairing surface defects; ② it acts as an in-situ pore-forming agent, constructing abundant micropores and closed pores within the carbon matrix; ③ it acts as a sodium replenishment and pre-sodiumization agent. These synergistic effects play a crucial role in improving the first-cycle coulombic efficiency (ICE), and while improving the first-cycle coulombic efficiency, it also enhances the reversible cycle capacity and energy density of sodium-ion full batteries.

[0028] It should be noted that the sodium alkoxy group in this application readily dissociates in organic solvents, releasing highly reactive sodium ions. These ions, along with organic anions, form a weak coordination structure, generating strong electrostatic attraction and chemical coordination with the abundant oxygen-containing functional groups and defect sites on the surface of activated carbon, significantly improving adsorption efficiency and distribution uniformity. In contrast, metallic sodium reacts violently and is difficult to disperse uniformly, inorganic sodium salts have low solubility and are prone to crystallization, while molten sodium systems pose safety hazards and poor interfacial wettability. Sodium alkoxy group combines good solubility, controllable reactivity, and excellent affinity for carbon materials, making it more conducive to the efficient loading and stable anchoring of sodium ions in the carbon matrix, providing a reliable foundation for the multiple synergistic effects during subsequent high-temperature carbonization.

[0029] The mass ratio of carbon precursor to activator described in this application is (1-6):1. A ratio that is too low leads to insufficient pore development, while a ratio that is too high causes excessive etching and damage to the carbon framework. An appropriate ratio of carbon precursor to activator can optimize the micropore / closed-pore ratio and the orderliness of the carbon layer, balancing sodium storage sites and electron transport pathways, thereby improving reversible capacity, first-time efficiency, and A2. D / A G The carbon precursor and activator can be mixed by ball milling. For example, the ball mill used for ball milling is set to revolve at 80-120 rpm and rotate at 270-330 rpm, running alternately in both directions for 1.8-2.2 hours, with a total running time of 11-13 hours.

[0030] The low-temperature carbonization temperature described in this application is 700-900℃. A moderately low temperature is more conducive to retaining sodium-loving groups, providing conditions for the efficient adsorption of sodium ions.

[0031] In this application, the mass / molar ratio of the activated carbon material to the sodium alkoxy group in the mixed slurry is 12:(0.03-0.5) (g / mol), preferably 12:(0.05-0.2) (g / mol), more preferably 12:(0.08-0.15) (g / mol), for example 12:0.1 (g / mol). This range can balance the adsorption capacity and distribution uniformity of sodium alkoxy group in the activated carbon material, providing a structural basis for simultaneous catalysis, pore formation, and pre-sodiumization at high temperatures, thereby synergistically improving the first-cycle coulombic efficiency, reversible capacity, and structural stability. If the relative content of sodium alkoxy group is too low, the sodium supply is insufficient, making it difficult to effectively catalyze graphitization, repair surface defects, and construct closed-pore structures; if it is too high, it will lead to excessive precipitation or aggregation of sodium ions, causing side reactions, damaging the carbon skeleton, and increasing irreversible sodium loss during subsequent high-temperature carbonization.

[0032] In an optional embodiment, the carbon precursor is selected from at least one of biomass carbon materials, resin carbon materials, sugar carbon materials, and petroleum-based carbon materials; for example, the biomass carbon materials include at least one of coconut shells, straw, bamboo, etc.; the resin carbon materials include at least one of phenolic resins, polyaniline, polyacrylonitrile, etc.; the sugar carbon materials include at least one of glucose, sucrose, cellulose, etc.; and the petroleum-based carbon materials include at least one of anthracite, asphalt, etc.

[0033] In optional embodiments, the activator is selected from at least one of alkali metal hydroxides, acrylate polymers, inorganic oxyacids, transition metal chlorides, and trialkylamines; for example, the activator is selected from at least one of KOH, PMMA (polymethyl methacrylate), H3PO4, ZnCl2, and TEA (triethanolamine). By selecting different activators, the defect density and surface chemical properties of the carbon skeleton can be controlled, affecting the specific surface area, pore size distribution, and functional group content of the activated carbon after low-temperature carbonization. The activated carbon material prepared with the participation of the above activators can take into account both the adsorption capacity and binding stability of sodium ions, providing a structural basis for subsequent pre-sodiumization and closed-pore construction, and achieving a synergistic improvement in the first-cycle coulombic efficiency and closed-pore specific surface area.

[0034] In an optional embodiment, the mass concentration of activated carbon material in the mixed slurry is 5-45 g / L, preferably 10-15 g / L, for example 12 g / L; this concentration range is beneficial for the uniform dispersion of activated carbon material in the mixed slurry.

[0035] In an optional embodiment, the molar concentration of sodium alkoxy in the mixed slurry is 0.03-0.5 mol / L, optionally 0.05-0.2 mol / L, for example 0.1 mol / L; combined with the mass concentration of activated carbon material, this ensures that the activated carbon material can adsorb a sufficient amount of sodium ions; In an optional embodiment, the sodium alkoxy is a C1-C8 sodium alkoxy, optionally a C1-C4 sodium alkoxy, such as sodium ethoxide. C1-C8 sodium alkoxy combines good solubility, controllable dissociation, and affinity for carbon materials in organic solvents, avoiding the risk of violent reactions with metallic sodium and the low solubility problem of inorganic sodium salts.

[0036] For example, the preparation of the mixed slurry includes uniformly dispersing activated carbon material in a solution obtained after the reaction of metallic sodium with an organic solvent. For example, the dispersion method can be stirring or ultrasonic dispersion.

[0037] In an optional embodiment, the low-temperature carbonization process takes 0.5-2 hours and is carried out in an inert atmosphere to achieve thorough carbonization.

[0038] In an optional embodiment, the heating rate of the low-temperature carbonization is 0.5-3℃ / min. Slow heating is more conducive to uniform activation and reducing defects, which is beneficial to balancing high initial efficiency and structural stability.

[0039] In an optional embodiment, the material after low-temperature carbonization is further subjected to sequential washing, filtration, and drying to obtain activated carbon material. Exemplarily, the drying process can be one of vacuum drying, spray drying, or freeze drying. Purification removes residual activating agents and prevents impurities from interfering with the sodium reaction during the high-temperature stage, which is beneficial for balancing high ICE (internal emission temperature) and reversible capacity.

[0040] In an optional embodiment, the solvent is selected from at least one of alcohol solvents, organic acid solvents, and ammonia solvents. For example, the alcohol solvent includes at least one of methanol, ethanol, and ethylene glycol; the organic acid solvent includes at least one of formic acid, acetic acid, and propionic acid; and the ammonia solvent includes liquid ammonia.

[0041] In an optional embodiment, the carbonization temperature of the high-temperature carbonization is 800-1400℃, the carbonization time is 0.5-2h, and the atmosphere is an inert atmosphere; sufficient high temperature is a necessary condition for driving sodium-catalyzed graphitization, repairing defects and stabilizing the closed-pore structure, and directly affects the first efficiency and energy density.

[0042] In an optional embodiment, the heating rate of the high-temperature carbonization is 0.5-3℃ / min. Appropriately reducing the heating rate can improve the AD / AG ratio and the first-week coulombic efficiency while taking into account the reaction efficiency.

[0043] This invention also provides a hard carbon material, prepared by any one of the preparation methods described in the foregoing embodiments, having the following structure: Figure 2 As shown.

[0044] In an optional embodiment, the average closed-pore diameter of the hard carbon material is 1.6-3.0 nm.

[0045] In an optional embodiment, the hard carbon material A D / A G It is 1.1-1.7.

[0046] In an optional embodiment, the specific surface area of ​​the closed pores in the hard carbon material is 200-450 m². 2 g -1 The available location is 310-350 m. 2 g -1 .

[0047] This invention also provides a negative electrode sheet, comprising the hard carbon material described in the foregoing embodiments. Exemplarily, the negative electrode sheet includes a substrate and a negative electrode coating disposed on the substrate. The substrate can be a copper foil current collector. The negative electrode coating may further include a conductive agent and a binder. The conductive agent can be carbon black, carbon nanotubes, or graphene to construct a conductive network; the binder can be sodium alginate, sodium carboxymethyl cellulose, or styrene-butadiene rubber; a small amount of wetting agent, such as deionized water, is added to some systems.

[0048] This invention also provides a battery comprising the negative electrode sheet described in the foregoing embodiments.

[0049] For example, the battery is a sodium-ion secondary battery, and the positive electrode of the sodium-ion secondary battery includes one or more of Prussian blue analogues, transition metal oxides, and polyanionic compounds; the electrolyte solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the sodium salt includes one or more of NaPF6, NaBF4, NaDFOB, NaCF3SO3, and NaClO4; and the separator includes one or more of polyolefin composite separators, glass fiber filter paper separators, and organic polymer nonwoven fabric separators.

[0050] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0051] Example 1 This embodiment provides a method for preparing hard carbon materials, specifically including the following steps: (1) 1.8g of carbon precursor and activator were placed in a ball mill jar and ball milled and mixed in a mass ratio of 3:1. After being mixed evenly, the mixture was placed in a tube furnace for low-temperature carbonization. Then, the carbon material was obtained by repeatedly washing, filtering and drying with deionized water to remove residues and activator. 1.2g of activated carbon material was taken for later use.

[0052] The carbon precursor was phenolic resin (brand: Adamas, RG grade, CAS: 9003-35-4), the activator was ZnCl2, and the ball mill used for ball milling was set to revolve at 100 rpm and rotate at 300 rpm, running alternately in both directions for 2 hours, with a total running time of 12 hours; the low-temperature carbonization was carried out under Ar atmosphere protection, with the temperature rising to 800℃ at 0.5℃ / min and held for 2 hours.

[0053] (2) Dissolve 0.23g of metallic sodium in 100ml of anhydrous ethanol to prepare c(Na) + () is a 0.1 mol / L sodium-containing solution.

[0054] (3) Place the activated carbon material prepared in step (1) into the sodium-containing solution in step (2), disperse it by ultrasonication, and let it stand for 8 hours to allow the activated carbon material to fully adsorb metal ions. Then, use vacuum drying to evaporate the excess solvent. The molar ratio of the activated carbon material to sodium ions is 12:0.1 (g / mol).

[0055] (4) High-temperature carbonization: Under Ar atmosphere protection, the temperature is increased to 1400℃ at 0.5℃ / min and held for 2h to obtain hard carbon material.

[0056] Example 2 The difference between this embodiment and Embodiment 1 is that in step (1), the carbon precursor is glucose and the activator is polymethyl methacrylate (PMMA, brand Adamas, model: Mw-350000, CAS: 9011-14-7).

[0057] Example 3 The difference between this embodiment and Embodiment 1 is that the carbon precursor in step (1) is corn stalk and the activator is potassium hydroxide (KOH).

[0058] Example 4 The difference between this embodiment and embodiment 1 is that the carbon precursor in step (1) is anthracite and the activator is H3PO4.

[0059] Example 5 The only difference between this embodiment and Embodiment 1 is that the mass ratio of carbon precursor to activator in step (1) is 6:1.

[0060] Example 6 The only difference between this embodiment and Embodiment 1 is that the mass ratio of carbon precursor to activator in step (1) is 1:1.

[0061] Comparative Example 1 The only difference between this embodiment and Embodiment 1 is that there is no activator in step (1).

[0062] Comparative Example 2 The only difference between this embodiment and embodiment 3 is that the low-temperature carbonization temperature in step (1) is 400°C.

[0063] Comparative Example 3 The only difference between this embodiment and Embodiment 3 is that the amount of metallic sodium used in step (2) is changed, so that the concentration of activated carbon material in the sodium-containing solution in step (3) is: Na in the sodium-containing solution + The concentrations were 12:0.6 (g / L:mol / L), while keeping the solution volume constant.

[0064] Comparative Example 4 The only difference between this embodiment and Embodiment 3 is that the amount of metallic sodium used in step (2) is changed, so that the concentration of activated carbon material in the sodium-containing solution in step (3) is: Na in the sodium-containing solution + The concentrations were 48:0.1 (g / L:mol / L), while keeping the solution volume constant.

[0065] Comparative Example 5 The only difference between this comparative example and Example 3 is that the low-temperature carbonization temperature in step (1) is 1200°C.

[0066] Comparative Example 6 The only difference between this embodiment and embodiment 3 is that sodium chloride aqueous solution is used in step (2), the solution volume remains unchanged, and the concentration is 0.1 mol / L.

[0067] Table 1 shows some of the preparation conditions and parameters of the hard carbon anode materials of the above embodiments and comparative examples.

[0068] A D / A G It is the ratio of the area of ​​peak D to peak G in the Raman spectrum, where A D The area of ​​peak D corresponds to the disordered carbon structure and defects; A G Let G be the area of ​​the peak, corresponding to the sp² ordered graphite structure. A D / A G The larger the ratio, the more defects there are and the higher the disorder; the smaller the ratio, the higher the graphitization and the better the order. This ratio is used to characterize the degree of disorder in the microstructure of hard carbon.

[0069] A D / A G Testing method: The hard carbon materials prepared in the above examples and comparative examples were tested using a Raman spectroscopy instrument. Laser wavelength: 785 nm, test range wavenumber: 1000-2000 cm⁻¹ -1 The test results were then processed using data processing software on a 1350 cm [scale / section]. -1 and 1580cm -1 The corresponding D and G peaks were subjected to area fitting.

[0070] Closed-cell specific surface area: SAXS (small-angle X-ray scattering) is a conventional testing method to test the closed-cell specific surface area of ​​hard carbon.

[0071] Table 1

[0072] The preparation of sodium-ion batteries using the hard carbon materials prepared in the above embodiments and comparative examples as negative electrode active materials specifically includes the following steps: Negative electrode sheet: The above-mentioned negative electrode active material, conductive agent (carbon black), and binder (sodium alginate) are uniformly mixed in a mass ratio of 95:3:2, and deionized water is added to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector copper foil, with an areal density of 1.8 mg / cm³. -2 The material is vacuum dried at 80℃ for 12 hours to form a negative electrode active material layer. Finally, it is rolled and punched to obtain the negative electrode sheet.

[0073] Sodium-ion battery: The Na sheet used as the counter electrode and the above-mentioned negative electrode sheet were assembled into CR2032 coin cells in a glove box with a water oxygen content of less than 0.01ppm. The electrolyte used was a mixture of 1M NaClO4 and ethylene carbonate (EC) and dimethyl carbonate (DMC) in equal volume ratio, and 5% fluoroethylene carbonate (FEC) was added as an additive.

[0074] First week Coulomb efficiency test The test conditions were: current density of 0.1C, voltage range of 0V to 2V. First, a constant current discharge test was performed, and the discharge capacity was recorded as C0. Then, a constant current charge test was performed, and the charging capacity was recorded as C1. The coulombic efficiency ICE (%) for the first cycle was calculated as the charge capacity / discharge capacity x 100%. The test results are shown in Table 1.

[0075] As can be seen from Examples 1-4, this scheme is adaptable to various carbon material precursors, and works at suitable carbonization temperatures and Na... + Under certain concentration conditions, the metal ions adsorbed by activated carbon can catalyze graphitization, improve the ordering of the carbon layer and repair surface defects. The final optimized product has a suitable degree of graphitization and closed-pore specific surface area. No SEI film is generated in the closed-pore cavity, which can reduce irreversible sodium loss and improve the first-cycle coulombic efficiency of hard carbon materials.

[0076] A comparison of Examples 1, 5, and 6 with Comparative Example 1, and of Example 3 with Comparative Examples 2 and 5, reveals that the proportion of activator and the low-temperature carbonization temperature significantly affect the adsorption capacity of the prepared activated carbon. When the proportion of activator is insufficient / excessive, or when the low-temperature carbonization temperature is too low / too high, the adsorption capacity of the activated carbon is affected, and it cannot effectively adsorb sodium ions from sodium-containing organic solutions. This affects the graphitization process and the closed-pore specific surface area during subsequent carbonization, negatively impacting the first-cycle coulombic efficiency.

[0077] As can be seen from Examples 3 and Comparative Examples 3 and 4, if the sodium ion content in the sodium-containing solution is too high, the activated carbon cannot adsorb all the redundant sodium ions. The excess sodium ions are deposited on the surface of the hardened particles and in the gaps between the particles, which increases the side reactions with the electrolyte and aggravates the reversible sodium loss. If the sodium ion content in the sodium-containing solution is too low, the activated carbon cannot adsorb enough sodium ions, resulting in incomplete catalysis, affecting the degree of graphitization, and causing a decrease in the coulombic efficiency in the first week.

[0078] Compared with Comparative Example 6, the hard carbon material prepared using the organic solvent of the present invention is more thoroughly dispersed in the organic solvent than the traditional solution, and has more sufficient contact with sodium ions in the organic solution. It has better adsorption capacity and effect, which is more beneficial for subsequent sodium ion catalytic graphitization.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon material, characterized in that, It includes the following three steps: (1) The mixture of carbon precursor and activator is carbonized at low temperature to obtain activated carbon material; (2) The mixed slurry composed of the activated carbon material, sodium alkoxy and solvent is dried to obtain sodium-impregnated activated carbon material; (3) The sodium-impregnated activated carbon material is carbonized at high temperature to obtain the hard carbon material; The mass ratio of the carbon precursor to the activator is (1-6):1; The low-temperature carbonization temperature is 700-900℃; In the mixed slurry, the mass / molar ratio of the activated carbon material to the sodium alkoxy is 12:(0.03-0.5) (g / mol).

2. The method for preparing hard carbon material according to claim 1, characterized in that, In the mixed slurry, the mass / molar ratio of the activated carbon material to the sodium alkoxy group is 12:(0.05-0.2) (g / mol).

3. The method for preparing hard carbon material according to claim 1, characterized in that, The carbon precursor is selected from at least one of biomass-based carbon materials, resin-based carbon materials, sugar-based carbon materials, and petroleum-based carbon materials; And / or, the activator is selected from at least one of alkali metal hydroxides, acrylate polymers, inorganic oxyacids, transition metal chlorides, and trialkylamines.

4. The method for preparing hard carbon material according to claim 1, characterized in that, The mass concentration of activated carbon material in the mixed slurry is 5-45 g / L.

5. The method for preparing hard carbon material according to claim 1, characterized in that, The molar concentration of sodium alkoxy in the mixed slurry is 0.03-0.5 mol / L.

6. The method for preparing hard carbon material according to claim 1, characterized in that, The sodium alkoxy group is a C1-C8 sodium alkoxy group.

7. The method for preparing hard carbon material according to any one of claims 2-6, characterized in that, In the mixed slurry, the mass / molar ratio of the activated carbon material to the sodium alkoxy group is 12:(0.08-0.15) (g / mol). And / or, the concentration of activated carbon material in the mixed slurry is 10-15 g / L; And / or, the concentration of sodium alkoxy in the mixed slurry is 0.05-0.2 mol / L; And / or, the sodium alkoxy is a C1-C4 sodium alkoxy.

8. The method for preparing hard carbon material according to claim 7, characterized in that, In the mixed slurry, the mass / molar ratio of the activated carbon material to the sodium alkoxy group is 12:0.1 (g / mol). And / or, the carbonization time of the low-temperature carbonization is 0.5-2 hours and the atmosphere is an inert atmosphere; And / or, the heating rate for the low-temperature carbonization is 0.5-3℃ / min; And / or, it also includes sequentially washing, filtering and drying the material after low-temperature carbonization to obtain activated carbon material.

9. The method for preparing hard carbon material according to claim 1, characterized in that, The solvent is selected from at least one of alcohol solvents, organic acid solvents, and ammonia solvents.

10. The method for preparing hard carbon material according to claim 1, characterized in that, The high-temperature carbonization process involves a carbonization temperature of 800-1400℃, a carbonization time of 0.5-2 hours, and an inert atmosphere. And / or, the heating rate of the high-temperature carbonization is 0.5-3℃ / min.

11. A hard carbon material, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

12. The hard carbon material according to claim 11, characterized in that, The average diameter of the closed pores in the hard carbon material is 1.6-3.0 nm.

13. The hard carbon material according to claim 11, characterized in that, The hard carbon material A D / A G It is 1.1-1.

7.

14. The hard carbon material according to claim 11, characterized in that, The specific surface area of ​​the closed pores in the hard carbon material is 200-450 m². 2 g -1 .

15. A negative electrode sheet, characterized in that, Includes the hard carbon material as described in any one of claims 11-14.

16. A battery, characterized in that, Includes the negative electrode sheet as described in claim 15.

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