Hard carbon material, preparation method thereof and battery

Abstract

The invention relates to the field of batteries, in particular to a hard carbon negative electrode material, a preparation method thereof and a battery. The preparation method of the hard carbon material comprises the following steps: mixing aromatic hydrocarbon oil and formamide, extracting and separating to obtain a formamide soluble substance, and distilling the formamide soluble substance to obtain a first product; mixing the first product with a solvent, extracting and separating to obtain a first solvent insoluble substance; mixing the first solvent insoluble substance with a solvent, extracting and separating to obtain a second solvent insoluble substance; mixing the second solvent insoluble substance with a solvent, and performing extraction and separation to obtain a third solvent insoluble substance; and carrying out carbonization treatment on the third solvent insoluble substance to obtain the hard carbon material. The hard carbon material provided by the invention is low in sulfur content, good in hard carbon cyclicity and low in high-temperature self-discharge.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a hard carbon material, a preparation method thereof, and a battery. Background Art

[0002] At present, with the development of sodium batteries, hard carbon has attracted much attention as the main material for the negative electrode of sodium batteries. Generally speaking, in the synthesis of hard carbon materials, the precursor is generally composed of oxygen-rich substances (or hydrogen-deficient materials) such as resin, biomass, and coal-based materials, and these precursors are sintered at a temperature exceeding 1000°C to form hard carbon. Generally speaking, the degree of cross-linking of organic macromolecules in hard carbon precursors is high, and the basic structural units are not easy to form parallel arrangements, so it is difficult to graphitize at any temperature. From a macroscopic structural point of view, hard carbon can retain the structural morphology of its precursor, so the selection and heat treatment of the precursor are particularly important.

[0003] However, as the industry matures and competition intensifies, the cost of hard carbon is trending downward. Therefore, whether it's the unstable consistency of biomass and the difficulty in controlling pore formation, the high cost and low yield of resin, the low performance and limited raw material cost of pitch, or the low cost but poor performance of anthracite, it's difficult to meet the material demand for large-scale industrialization of sodium batteries. Therefore, it is crucial to control costs from the source of precursors to reduce costs and increase efficiency.

[0004] Pitch has the advantages of outstanding cost-effectiveness, good structural adjustability and high carbon yield, so it is considered to be an ideal precursor to promote the large-scale production of hard carbon. However, the chemical composition and structure of asphalt are very complex, and the structural differences between different asphalt molecules may affect the structure and electrochemical properties of asphalt-derived hard carbon. In particular, the molecular properties and composition of asphalt vary with the source of crude oil and the production method, which is very unfavorable for the subsequent regulation of hard carbon structure and performance and large-scale production, and hinders further research on its "structure-activity relationship". The complexity of asphalt makes it challenging to rationally select hard carbon precursors. If the asphalt components are not precisely regulated, the first effect, capacity, rate and cycle of asphalt-based hard carbon are difficult to precisely control, and it is difficult to meet the needs of specific original scenarios. For example, when asphalt-based hard carbon requires long cycles, the capacity and rate are neglected and are often relatively low. This is because the carbon microcrystalline layer spacing d (002) The reason for this is that the electrolyte solvent, lithium salt, and formation process are often used to adjust the SEI film to improve rate and capacity. However, research on pitch-based components and hard carbon structures is relatively limited.

[0005] Therefore, it is urgent to fully understand the composition and structural characteristics of asphalt starting from asphalt raw materials. It is of great significance to examine the influence of raw material composition on the formation of its derived hard carbon structure and electrochemical performance. Summary of the Invention

[0006] In view of this, the present invention is dedicated to providing a hard carbon material and a preparation method thereof and a battery, wherein the hard carbon material has a high hard carbon yield and good rate performance.

[0007] In order to solve the above technical problems, this application is implemented as follows:

[0008] The present invention provides a method for preparing a hard carbon material, comprising the following steps:

[0009] (1) mixing aromatic oil and formamide, extracting and separating to obtain formamide soluble matter, and distilling the formamide soluble matter to obtain a first product;

[0010] (2) mixing the first product with a solvent, extracting and separating the first product to obtain a first solvent-insoluble substance;

[0011] (3) mixing the first solvent-insoluble matter with the solvent, extracting and separating the matter to obtain the second solvent-insoluble matter;

[0012] (4) mixing the second solvent-insoluble matter with the solvent, extracting and separating the matter to obtain a third solvent-insoluble matter;

[0013] (5) Carbonizing the third solvent-insoluble matter to obtain a hard carbon material.

[0014] Preferably, in the above-mentioned method for preparing a hard carbon material, in step (1), the softening point of the aromatic oil is 0 to 219°C;

[0015] And / or, in step (1), the aromatic oil includes at least one of ethylene tar, catalytic cracking slurry, coal tar and bio-tar.

[0016] Preferably, in the above-mentioned method for preparing a hard carbon material, in step (1), the usage ratio of the aromatic oil to the formamide is 300-500 g: 1500-3000 mL;

[0017] And / or, in step (1), the extraction temperature is 70-90° C., and the extraction time is 50-70 min.

[0018] Preferably, in the above-mentioned method for preparing a hard carbon material, in step (2), the usage ratio of the first product to the solvent is 70-90 g: 300-500 mL;

[0019] And / or, in step (2), the solvent comprises at least one of petroleum ether, n-pentane, n-hexane, n-heptane, n-octane, n-octane, cyclohexane and cyclopentane; and the medium boiling range of the petroleum ether is 30-60°C.

[0020] Preferably, in the above-mentioned method for preparing a hard carbon material, in step (2), the extraction temperature is 50 to 70° C., and the extraction time is 20 to 40 minutes.

[0021] Preferably, in the above-mentioned method for preparing a hard carbon material, in step (3), the ratio of the amount of the first solvent-insoluble matter to the solvent is 30-50 g: 100-300 mL;

[0022] and / or, in step (3), the solvent comprises at least one of chloroform, diethyl ether, dipropyl ether, toluene, benzene, p-xylene, chlorobenzene, tetrahydrofuran and o-dichlorobenzene;

[0023] And / or, in step (3), the extraction temperature is 50-70° C., and the extraction time is 50-70 min.

[0024] Preferably, in the above-mentioned method for preparing a hard carbon material, in step (4), the ratio of the amount of the second solvent-insoluble matter to the solvent is 10-30 g: 50-200 mL;

[0025] and / or, in step (4), the solvent comprises at least one of sulfolane, propionitrile, dimethyl sulfoxide, aniline, acetone and acetic anhydride;

[0026] And / or, in step (4), the extraction temperature is 70-90° C., and the extraction time is 50-70 min.

[0027] Preferably, in the above-mentioned method for preparing a hard carbon material, in step (5), the carbonization treatment is a segmented carbonization treatment;

[0028] The conditions of the first carbonization treatment in the staged carbonization treatment are as follows: the atmosphere is air and / or oxygen atmosphere, the flow rate of the atmosphere is 300-400 mL / min, the heating rate is 5-10°C / min, the temperature is 280-490°C, and the time is 0.5-8h;

[0029] The conditions for the second carbonization treatment in the staged carbonization treatment are as follows: the atmosphere is an inert gas, the flow rate of the atmosphere is 0.05-3 L / min, the heating rate is 0.1-10° C. / min, the temperature is 1000-1600° C., and the time is 0.5-17 h.

[0030] The present invention also provides a hard carbon material prepared by the method for preparing the hard carbon material.

[0031] The present invention also provides a battery, comprising a negative electrode sheet, wherein the negative electrode sheet comprises the hard carbon material.

[0032] Through the above technical solution, the beneficial technical effects of the present invention are:

[0033] The present invention adopts a four-stage solvent extraction process of formamide extraction - washing with petroleum ether or other solvents - washing with chloroform or other solvents - cyclopentane or other solvents, that is, the formamide soluble matter is subjected to three-stage washing to separate the asphalt component with high aromaticity, fewer and shorter alkyl side chains, and abundant polar oxygen and abundant polar pyrrole N pentacyclic functional groups. At the same time, because it is rich in polar O and N functional groups, its oxidation activity is enhanced, so that more oxygen can be obtained to construct a rich three-dimensional cross-linked structure, thereby limiting the rearrangement of the carbon layer during the carbonization process of the asphalt-based component, expanding the interlayer spacing, promoting the development of ultramicropores and the formation of disordered structures, and further corresponding to a larger d (002) and smaller Lc parameters, resulting in a high-rate hard carbon precursor. Furthermore, the pitch component, having already separated most of the light components during the previous extraction step, offers a high product yield. Furthermore, the sulfolane extraction and washing process reduces the sulfur content in organic matter, enhancing the hard carbon material's recyclability and lowering the self-discharge rate of the hard carbon sodium electrode at high temperatures.

[0034] Among various organic solvents, formamide has the highest polarity, extracting the target component first, followed by sequential extraction and washing with more negative solvents. Among them, mid-boiling-range petroleum ether has the lowest polarity and can extract and separate light components. Chloroform has an intermediate polarity and can extract some of the more polar components insoluble in the first solvent, but the carbonization yield of these components is extremely low (<30%). Therefore, sulfolane is used to further extract and wash the insoluble components in the second solvent. Sulfolane has a slightly higher polarity than chloroform, and the extracted components have a larger molecular weight, and most of the molecules are polar or contain sulfur.

[0035] Therefore, according to the proposed four-stage solvent extraction sequence of amide extraction-petroleum ether washing-chloroform washing-cyclopentane sulfone, a different extraction process for aromatic-rich oil components can be obtained, and the obtained components can be carbonized to obtain hard carbon with low sulfur content, good hard carbon cyclability, and low high-temperature self-discharge.

[0036] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention.

[0038] Figure 1 Shown is a process flow chart of the present invention. DETAILED DESCRIPTION

[0039] The present invention discloses a hard carbon material, a preparation method, and a battery. Those skilled in the art can refer to the contents herein and appropriately modify the process parameters to achieve the desired results. It is particularly important to note that all similar substitutions and modifications obvious to those skilled in the art are considered encompassed by the present invention. The methods and applications of the present invention have been described through preferred embodiments. It is clear that those skilled in the art can modify or appropriately alter and combine the methods and applications described herein to implement and apply the technology of the present invention without departing from the content, spirit, and scope of the present invention.

[0040] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0042] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0043] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0044] The present invention provides a method for preparing a hard carbon material, comprising the following steps:

[0045] (1) mixing aromatic oil and formamide, extracting and separating to obtain formamide soluble matter, and distilling the formamide soluble matter to obtain a first product;

[0046] (2) mixing the first product with a solvent, extracting and separating the first product to obtain a first solvent-insoluble substance;

[0047] (3) mixing the first solvent-insoluble matter with the solvent, extracting and separating the matter to obtain the second solvent-insoluble matter;

[0048] (4) mixing the second solvent-insoluble matter with the solvent, extracting and separating the matter to obtain a third solvent-insoluble matter;

[0049] (5) Carbonizing the third solvent-insoluble matter to obtain a hard carbon material.

[0050] In the present invention, in step (1), the softening point of the aromatic oil is preferably 0 to 219°C, more preferably 20 to 180°C, and even more preferably 25 to 150°C.

[0051] In the present invention, in step (1), the aromatic oil includes, but is not limited to, at least one of ethylene tar, catalytic cracking slurry, coal tar and bio-tar.

[0052] In the present invention, in step (1), the usage ratio of the aromatic oil to the formamide is preferably 300-500 g:1500-3000 mL, more preferably 350-450 g:1800-2500 mL, and even more preferably 400 g-2000 mL.

[0053] In the present invention, in step (1), the extraction temperature is preferably 70-90°C, more preferably 75-85°C, and more preferably 80°C; the extraction time is preferably 50-70 min, more preferably 55-65 min, and more preferably 60 min.

[0054] In the present invention, in step (1), the separation process is: filtering while hot after the extraction is completed.

[0055] In the present invention, in step (2), the usage ratio of the first product to the solvent is preferably 70-90 g:300-500 mL, more preferably 75-85 g:350-450 mL, and more preferably 80 g:400 mL.

[0056] In the present invention, in step (2), the solvent includes at least one of petroleum ether, n-pentane, n-hexane, n-heptane, n-octane, n-octane, cyclohexane and cyclopentane.

[0057] In the present invention, the medium boiling range of the petroleum ether is preferably 30-60°C.

[0058] In the present invention, in step (2), the extraction temperature is preferably 50-70°C, more preferably 55-65°C, and more preferably 60°C; the extraction time is preferably 20-40 min, more preferably 25-35 min, and more preferably 30 min.

[0059] In the present invention, in step (2), the separation process is: filtering while hot after the extraction is completed.

[0060] In the present invention, in step (3), the usage ratio of the first solvent-insoluble matter to the solvent is preferably 30-50 g:100-300 mL, more preferably 35-45 g:150-250 mL, and more preferably 50 g:200 mL.

[0061] In the present invention, in step (3), the solvent comprises at least one of chloroform, diethyl ether, dipropyl ether, toluene, benzene, p-xylene, chlorobenzene, tetrahydrofuran and o-dichlorobenzene;

[0062] In the present invention, in step (3), the extraction temperature is preferably 50-70°C, more preferably 55-65°C, and more preferably 60°C; the extraction time is preferably 50-70 min, more preferably 55-65 min, and more preferably 60 min.

[0063] In the present invention, in step (3), the separation process is: after the extraction is completed, the temperature is lowered to below the boiling point of the solvent and then filtered while hot.

[0064] In the present invention, in step (4), the usage ratio of the second solvent-insoluble matter to the solvent is preferably 10-30 g:50-200 mL, more preferably 15-25 g:80-150 mL, and even more preferably 20 g:100 mL.

[0065] In the present invention, in step (4), the solvent comprises at least one of sulfolane, propionitrile, dimethyl sulfoxide, aniline, acetone and acetic anhydride;

[0066] In the present invention, in step (4), the extraction temperature is preferably 70-90°C, more preferably 75-85°C, and more preferably 80°C; the extraction time is preferably 50-70 min, more preferably 55-65 min, and more preferably 60 min.

[0067] In the present invention, in step (5), the carbonization treatment is a segmented carbonization treatment;

[0068] The conditions for the first carbonization treatment in the staged carbonization treatment are as follows: the atmosphere is preferably air and / or oxygen atmosphere, the flow rate of the atmosphere is preferably 300-400 mL / min, more preferably 310-380 mL / min, more preferably 320-350 mL / min; the heating rate is preferably 5-10°C / min, more preferably 6-9°C / min, more preferably 7-8°C / min; the temperature is preferably 280-490°C, more preferably 300-450°C, more preferably 350-400°C; the time is preferably 0.5-8 h, more preferably 1-6 h, more preferably 2-4 h;

[0069] The first carbonization process also includes turning; the turning angle rate is 180° / min.

[0070] The conditions for the second carbonization treatment in the staged carbonization treatment are as follows: the atmosphere is preferably an inert gas, and the inert atmosphere is preferably at least one of nitrogen, argon, helium and neon; the flow rate of the atmosphere is preferably 0.05 to 3 L / min, more preferably 0.5 to 2.5 L / min, and more preferably 1 to 2 L / min; the heating rate is preferably 0.1 to 10°C / min, more preferably 1 to 8°C / min, and more preferably 2 to 5°C / min; the temperature is preferably 1000 to 1600°C, more preferably 1100 to 1500°C, and more preferably 1200 to 1400°C; the time is preferably 0.5 to 17h, more preferably 2 to 15h, and more preferably 5 to 12h.

[0071] The present invention also provides a hard carbon material prepared by the method for preparing the hard carbon material.

[0072] The present invention also provides a battery, comprising a negative electrode sheet, wherein the negative electrode sheet comprises the hard carbon material.

[0073] The present invention is further described in detail below by way of examples. The raw materials used in the examples can all be obtained through commercial sources.

[0074] Example 1

[0075] The method for preparing a hard carbon negative electrode material comprises the following steps:

[0076] (1) 400 g of ethylene tar (softening point: 25° C.) and 2000 mL of formamide were mixed, stirred and extracted at 80° C. for 60 min, and then filtered and separated while hot to obtain formamide-soluble matter, which was then distilled to obtain a first product;

[0077] (2) 80 g of the first product was mixed with 400 mL of petroleum ether having a medium boiling range of 30 to 60° C., and the mixture was stirred and extracted at 60° C. for 30 min. The mixture was filtered and separated while hot to obtain the first solvent-insoluble matter;

[0078] (3) 40 g of the first solvent-insoluble matter was mixed with 200 mL of chloroform, and the mixture was stirred and extracted at 60° C. for 60 min. The mixture was then cooled to below the boiling point of chloroform and filtered while hot to obtain the second solvent-insoluble matter.

[0079] (4) 20 g of the second solvent-insoluble matter was mixed with 100 mL of sulfolane, and the mixture was stirred and extracted at 80° C. for 60 min, and then filtered while hot to obtain the third solvent-insoluble matter;

[0080] (5) The third solvent-insoluble matter was heated to 390°C at a heating rate of 5°C / min in an air atmosphere, kept warm and flipped (the flipping angle rate was 180° / min) for carbonization treatment for 3 hours; then, in a nitrogen atmosphere with a flow rate of 1 L / min, the temperature was further increased to 1350°C at a heating rate of 5°C / min and kept warm for carbonization treatment for 2 hours to obtain a hard carbon material.

[0081] Example 2

[0082] The method for preparing the hard carbon negative electrode material is different from that of Example 1 in that:

[0083] In step (1), the softening point of ethylene tar is 15°C.

[0084] The rest are the same as in Example 1.

[0085] Example 3

[0086] The method for preparing the hard carbon negative electrode material is different from that of Example 1 in that:

[0087] In step (1), the softening point of ethylene tar is 205°C.

[0088] The rest are the same as in Example 1.

[0089] Example 4

[0090] The method for preparing the hard carbon negative electrode material is different from that of Example 1 in that:

[0091] In step (2), petroleum ether is replaced by n-hexane.

[0092] The rest are the same as in Example 1.

[0093] Example 5

[0094] The method for preparing the hard carbon negative electrode material is different from that of Example 1 in that:

[0095] In step (3), chloroform is replaced by tetrahydrofuran.

[0096] The rest are the same as in Example 1.

[0097] Example 6

[0098] The method for preparing the hard carbon negative electrode material is different from that of Example 1 in that:

[0099] Step (4) does not exist; that is, the second solvent insoluble matter is heated to 390°C at a heating rate of 5°C / min in an air atmosphere, kept warm and turned over for carbonization treatment for 3 hours; then, in a nitrogen atmosphere with a flow rate of 1 L / min, the temperature is further increased to 1350°C at a heating rate of 5°C / min and kept warm for carbonization treatment for 2 hours to obtain a hard carbon material.

[0100] The rest are the same as in Example 1.

[0101] Example 7

[0102] The method for preparing the hard carbon material is different from that of Example 1 in that:

[0103] In step (5), the third solvent insoluble matter is carbonized for 3 hours by heating the temperature to 280°C at a heating rate of 5°C / min in an air atmosphere and keeping the temperature without turning over; then, the temperature is further increased to 1100°C at a heating rate of 5°C / min in a nitrogen atmosphere with a flow rate of 1 L / min and keeping the temperature for 2 hours to obtain a hard carbon material.

[0104] The rest are the same as in Example 1.

[0105] Example 8

[0106] The method for preparing the hard carbon material is different from that of Example 1 in that:

[0107] In step (5), the third solvent insoluble matter is heated to 390°C at a heating rate of 5°C / min in an air atmosphere and kept warm and turned over for carbonization treatment for 3 hours; then, in a nitrogen atmosphere with a flow rate of 1 L / min, the temperature is further increased to 1100°C at a heating rate of 5°C / min and kept warm for carbonization treatment for 0.5 hours to obtain a hard carbon material.

[0108] The rest are the same as in Example 1.

[0109] Example 9

[0110] The method for preparing the hard carbon material is different from that of Example 1 in that:

[0111] In step (5), the third solvent insoluble matter is heated to 390°C at a heating rate of 5°C / min in an air atmosphere and then kept heated and turned over for carbonization treatment for 3 hours; then, in a nitrogen atmosphere with a flow rate of 1 L / min, the temperature is further increased to 1600°C at a heating rate of 5°C / min and kept heated for carbonization treatment for 8 hours to obtain a hard carbon material.

[0112] The rest are the same as in Example 1.

[0113] Comparative Example 1

[0114] A method for preparing a hard carbon material comprises the following steps:

[0115] (1) 400 g of ethylene tar (softening point: 25° C.) and 2000 mL of formamide were mixed, and the mixture was stirred and extracted at 80° C. for 60 min. The mixture was then filtered and separated while hot to obtain a formamide-soluble substance, which was then distilled to obtain a first product;

[0116] (2) 80 g of the first product was mixed with 400 mL of toluene, and the mixture was stirred and extracted at 60° C. for 30 min, and filtered while hot to obtain the first solvent-insoluble matter;

[0117] (3) 40 g of the first solvent-insoluble matter was mixed with 200 mL of tetrahydrofuran, and the mixture was stirred and extracted at 60° C. for 60 min. The mixture was then cooled to below the boiling point of chloroform and filtered while hot to obtain the second solvent-insoluble matter.

[0118] (5) The second solvent-insoluble matter was heated to 390°C at a heating rate of 5°C / min in an air atmosphere, kept warm and flipped (the flipping angle rate was 180° / min) for carbonization treatment for 3 hours; then, in a nitrogen atmosphere with a flow rate of 1 L / min, the temperature was further increased to 1350°C at a heating rate of 5°C / min and kept warm for carbonization treatment for 2 hours to obtain a hard carbon material.

[0119] Comparative Example 2

[0120] The method for preparing the hard carbon material is different from that of Example 1 in that:

[0121] In step (4), sulfolane is replaced by ethanol.

[0122] Test Example 1

[0123] 1. Preparation of batteries

[0124] The hard carbon negative electrode material prepared in the embodiment and the comparative example, the conductive agent conductive carbon black, the binder styrene butadiene rubber and the binder carboxymethyl cellulose were homogenized in a mass ratio of 95.5:1.5:1.5:1.5, and dried after coating to obtain a negative electrode sheet with a compaction degree of 1.05 g / cm 3 The negative electrode uses a sodium sheet with a thickness of 600μm, and an electrolyte is added (electrolyte composition: EC:PC:DMC (0.45:0.45:0.1) + 1M NaClO4) to assemble it into a 2032 button battery.

[0125] 2. Electrochemical performance test

[0126] Test charge and discharge system: In the range of 0-2.5V, first use 0.1C constant current to 2.5V, then use 2.5V constant voltage until the current is less than 0.02C. After 2 cycles, change to 1.0CC / 1.0CD. Continue the cycle for 50 cycles before removing the battery.

[0127] Rate Test: The battery was tested for rate discharge performance at different current densities (1.0C, 2C, 3C, 5C, 6C, and 8C). The cell was first fully charged at 1C (0-2.0V), allowed to rest for 30 minutes, and then discharged to a cutoff voltage of 2.0V. The test results are shown in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] Straight-through yield = m (target product after carbonization) / m (aromatic oil) *%.

[0132] As shown in Table 1, the higher the content of colloid and asphaltene in the raw material, the higher the yield of asphalt through the process. This is because the content of heavy components has little effect on the extraction and washing process, thereby improving the yield of through carbonization. At the same time, the corresponding microcrystalline interlayer spacing d (002) The parameters become slightly smaller, Lc becomes slightly larger, the capacity becomes smaller, and the circulation becomes better. The opposite is true. After formamide extracts and separates the corresponding components in the extraction, the content of medium and light components is greatly reduced during the subsequent washing of insoluble matter. Compared with the case of only two-stage extraction, the straight-through carbonization yield is lower, but the components are more concentrated and the circulation performance is better. The opposite is true. Adding a pre-oxidation step has a greater impact on improving the product yield. The higher the carbonization temperature, the more unstable bonds are broken, the lower the component yield after carbonization, the larger the pore volume, the lower the specific surface area, the lower the capacity, and the greater the rate. The opposite is true.

[0133] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon material, characterized in that: The following steps are involved: (1) mixing aromatic oil and formamide, extracting and separating to obtain formamide soluble matter, and distilling the formamide soluble matter to obtain a first product; (2) mixing the first product with a solvent, extracting and separating the first product to obtain a first solvent-insoluble substance; (3) mixing the first solvent-insoluble matter with the solvent, extracting and separating the matter to obtain the second solvent-insoluble matter; (4) mixing the second solvent-insoluble matter with the solvent, extracting and separating the matter to obtain a third solvent-insoluble matter; (5) Carbonizing the third solvent-insoluble matter to obtain a hard carbon material.

2. The method for preparing a hard carbon material according to claim 1, wherein: In step (1), the softening point of the aromatic oil is 0 to 219° C.; And / or, in step (1), the aromatic oil includes at least one of ethylene tar, catalytic cracking slurry, coal tar and bio-tar.

3. The method for preparing a hard carbon material according to claim 1, wherein: In step (1), the ratio of the aromatic oil to the formamide is 300-500 g: 1500-3000 mL; And / or, in step (1), the extraction temperature is 70-90° C., and the extraction time is 50-70 min.

4. The method for preparing a hard carbon material according to claim 1, wherein: In step (2), the ratio of the first product to the solvent is 70-90 g: 300-500 mL; And / or, in step (2), the solvent comprises at least one of petroleum ether, n-pentane, n-hexane, n-heptane, n-octane, n-octane, cyclohexane and cyclopentane; and the medium boiling range of the petroleum ether is 30-60°C.

5. The method for preparing a hard carbon material according to claim 1, wherein: In step (2), the extraction temperature is 50-70° C., and the extraction time is 20-40 minutes.

6. The method for preparing a hard carbon material according to claim 1, wherein: In step (3), the ratio of the first solvent-insoluble matter to the solvent is 30-50 g: 100-300 mL; and / or, in step (3), the solvent comprises at least one of chloroform, diethyl ether, dipropyl ether, toluene, benzene, p-xylene, chlorobenzene, tetrahydrofuran and o-dichlorobenzene; And / or, in step (3), the extraction temperature is 50-70° C., and the extraction time is 50-70 min.

7. The method for preparing a hard carbon material according to claim 1, wherein: In step (4), the ratio of the second solvent-insoluble matter to the solvent is 10-30 g: 50-200 mL; and / or, in step (4), the solvent comprises at least one of sulfolane, propionitrile, dimethyl sulfoxide, aniline, acetone and acetic anhydride; In step (4), the extraction temperature is 70 to 90° C., and the extraction time is 50 to 70 minutes.

8. The method for preparing a hard carbon material according to claim 1, wherein: In step (5), the carbonization treatment is a segmented carbonization treatment; The conditions of the first carbonization treatment in the staged carbonization treatment are as follows: the atmosphere is air and / or oxygen atmosphere, the flow rate of the atmosphere is 300-400 mL / min, the heating rate is 5-10°C / min, the temperature is 280-490°C, and the time is 0.5-8h; The conditions for the second carbonization treatment in the staged carbonization treatment are as follows: the atmosphere is an inert gas, the flow rate of the atmosphere is 0.05-3 L / min, the heating rate is 0.1-10° C. / min, the temperature is 1000-1600° C., and the time is 0.5-17 h.

9. A hard carbon material obtained by the method for preparing a hard carbon material according to any one of claims 1 to 8.

10. A battery comprising a negative electrode sheet, characterized in that: The negative electrode sheet includes the hard carbon material according to claim 9.

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