A hard carbon material and its preparation method and application

Abstract

The present invention relates to the technical field of hard carbon materials, and specifically discloses a hard carbon material, a preparation method thereof, and an application thereof. The present invention uses cheap ethylene tar as raw material, adopts a solvent of specific polarity to perform three-stage extraction on ethylene tar, and obtains aromatic substances and colloidal components with strong polarity in ethylene tar. The hard carbon material prepared by pre-carbonization and high-temperature carbonization using this component as a precursor has a large interlayer spacing, which helps to improve the specific capacity, rate performance and cycle stability of sodium ion batteries; in addition, the colloidal component can form a cross-linked structure in the hard carbon material, improve the conductivity and structural stability of the hard carbon material, and the cross-linked structure can also increase the surface roughness of the hard carbon material, improve the wettability of the electrolyte, and thus improve the charge and discharge performance of the sodium ion battery. The present invention provides a low-cost, high-performance hard carbon positive electrode material for sodium ion batteries, achieving the purpose of reducing costs and increasing efficiency.

Description

Technical Field

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

[0002] With the transformation of the global energy structure and the increasing emphasis on environmental protection, the research and development of new energy battery technologies has become a global focus. As core components in new energy vehicles, portable electronic devices, and large-scale energy storage, new energy batteries have experienced rapid development in recent years. With the rapid development of lithium-ion batteries and the shortage of lithium resources, sodium-ion batteries, which share similar electrochemical properties and abundant lithium resources, are gradually showing great commercial potential.

[0003] Hard carbon is a type of carbon that is difficult to graphitize. Due to the presence of a large number of heteroatoms such as H, O, and N in its precursor, the formation of crystalline regions during heat treatment is hindered, making it difficult to graphitize even at high temperatures above 2800°C. Its internal structure is highly irregular and disordered, mainly composed of disordered stacking of small-sized graphene sheets, which is generally described as a "falling card" model. Compared with graphite materials, hard carbon has more sodium ion storage sites and can better meet people's high energy storage requirements. In addition, hard carbon also has isotropic structural characteristics, and its interlayer spacing is larger than that of graphite (interlayer spacing d002>0.36nm), which facilitates the transport and diffusion of sodium ions. At the same time, it has good cycle performance and rate performance and low cost.

[0004] Asphalt has a high coking value, a wide range of sources, and a low price, and has obvious advantages as a hard carbon precursor. At present, the preparation method of conventional asphalt-based hard carbon materials is to oxidize the asphalt for pretreatment, solidify and cross-link to obtain a precursor material, and then carbonize and crush the precursor material under an inert atmosphere to obtain an asphalt-based hard carbon material. However, untreated asphalt is prone to form a graphite-like structure during the carbonization process. Therefore, when it is used to prepare hard carbon, the asphalt needs to be pretreated or pre-oxidized, which increases the preparation cost of asphalt-based hard carbon. As the price of lithium carbonate continues to decline, in order to increase the advantages of sodium-ion batteries, the development of lower-cost hard carbon is imperative. Summary of the Invention

[0005] To address the high production costs of existing pitch-based hard carbon materials and the need for further improvement in electrochemical performance, the present invention provides a hard carbon material, its preparation method, and its application. This invention uses inexpensive ethylene tar as a raw material, undergoes multi-stage extraction, and then pre-carbonizes and high-temperature carbonizes specific extracted components into a hard carbon material. The sodium-ion battery prepared using this hard carbon material as the positive electrode material exhibits advantages such as high compaction density, high initial efficiency, and high capacity retention, while effectively reducing the production cost of sodium-ion batteries. This material has broad application prospects in the field of sodium-ion batteries.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0007] In a first aspect, the present invention provides a method for preparing a hard carbon material, comprising the following steps:

[0008] S1, uniformly mixing ethylene tar and a primary extraction solvent, heating for extraction, and performing solid-liquid separation to obtain a primary extract; and removing the solvent from the primary extract to obtain a primary extract;

[0009] S2, uniformly mixing the primary extract and the secondary extraction solvent, heating for extraction, and solid-liquid separation to obtain a secondary raffinate;

[0010] S3, uniformly mixing the secondary raffinate and the tertiary extraction solvent, heating for extraction, cooling, solid-liquid separation, and drying to obtain a tertiary raffinate;

[0011] S4, pre-carbonizing the tertiary extract at 350° C. to 550° C., then high-temperature carbonizing at 750° C. to 1600° C. under an inert atmosphere, and crushing to obtain a hard carbon material;

[0012] Wherein, the primary extraction solvent includes at least one of quinoline, chloroform, 3-pentanone, 1,1-dichloroethane or cyclohexanone; the secondary extraction solvent is at least one of medium-boiling range petroleum ether, n-pentane, n-octane, cyclohexane or cyclopentane; in S3, the tertiary extraction solvent is at least one of n-butanol, isobutanol, amyl alcohol or isopropanol.

[0013] Compared with the prior art, the preparation method of the hard carbon material provided by the present invention uses cheap ethylene tar as raw material, adopts a solvent of specific polarity to perform three-stage extraction on the ethylene tar, and obtains aromatic substances and colloidal components in the ethylene tar. Most of these substances are strong polar components, and the structure contains more oxygen-containing functional groups. The hard carbon material prepared by pre-carbonization and high-temperature carbonization using this component as a precursor has a large interlayer spacing, which is conducive to the embedding and extraction of sodium ions, reduces the diffusion path of sodium ions in the hard carbon material, and provides more storage space for sodium ions. At the same time, it also helps to alleviate the volume expansion and contraction of the material during charging and discharging. In addition, the colloidal component can form a cross-linked structure in the hard carbon material, thereby improving the conductivity and structural stability of the hard carbon material. In addition, the cross-linked structure can form more micropores and defects, which can serve as sodium storage points to increase the storage capacity of sodium ions. The cross-linked structure can also increase the surface roughness of the hard carbon material, improve the wettability of the electrolyte, and thus improve the charging and discharging performance of the sodium ion battery.

[0014] Using the hard carbon material prepared by the present invention as the positive electrode material of sodium ion batteries can significantly improve the specific capacity, rate performance and cycle stability of sodium ion batteries, providing a low-cost, high-performance hard carbon positive electrode material for sodium ion batteries, achieving the purpose of reducing costs and increasing efficiency, which is of great significance for promoting the development of sodium ion batteries and has high promotion and application value.

[0015] It should be noted that the softening point (SP) of the ethylene tar in the present invention is less than 25°C.

[0016] Most asphalt is derived from the thermal polymerization and thermal polycondensation of ethylene tar. This invention uses inexpensive ethylene tar as a raw material, undergoes multi-stage extraction, and uses the extracted material as a precursor to prepare a hard carbon material. This not only significantly improves the electrochemical performance of the hard carbon material but also significantly reduces its production cost, providing a low-cost, high-performance cathode material for sodium-ion batteries.

[0017] Preferably, in S1, the primary extraction solvent is quinoline.

[0018] Furthermore, in S1, the temperature of the heating extraction is 70°C to 90°C, and the time of the heating extraction is 50min to 70min.

[0019] Furthermore, in S1, the mass volume ratio of the ethylene tar to the primary extraction solvent is 1 g:4 mL to 1 g:6 mL.

[0020] Preferably, in S1, the mass volume ratio of the ethylene tar to the primary extraction solvent is 1 g:5 mL.

[0021] Preferably, in S2, the secondary extraction solvent is medium-boiling-range petroleum ether.

[0022] Furthermore, the mass volume ratio of the primary extract and the secondary extraction solvent is 1g:2mL~1g:4mL.

[0023] Preferably, the mass volume ratio of the primary extract to the secondary extraction solvent is 1 g:3 mL.

[0024] Furthermore, in S2, the temperature of the heating extraction is 40°C to 60°C, and the time of the heating extraction is 20 minutes to 40 minutes.

[0025] Preferably, in S3, the tertiary extraction solvent is n-butanol.

[0026] Furthermore, in S3, the mass volume ratio of the secondary raffinate to the tertiary extraction solvent is 1 g:3 mL to 1 g:5 mL.

[0027] Preferably, in S3, the mass volume ratio of the secondary raffinate to the tertiary extraction solvent is 1 g:4 mL.

[0028] Furthermore, in S3, the temperature of the heating extraction is 50° C. to 70° C., and the time of the heating extraction is 50 min to 70 min.

[0029] It should be noted that, in S3, after cooling to a temperature lower than the boiling point of the tertiary extraction solvent, suction filtration is performed while hot to obtain a tertiary extraction residue.

[0030] It should be noted that, in the above S1 to S3, the extraction processes are all carried out in a stainless steel reactor at normal pressure, and stirring is performed during the extraction process.

[0031] Taking quinoline, mid-boiling range petroleum ether and n-butanol as examples, the principle of the extraction process in the present invention is as follows:

[0032] Ethylene tar is extracted with quinoline, and the quinoline soluble matter obtained by extraction excludes the components of quinoline insolubles, leaving only saturated parts, aromatic parts and gum components. After extraction with petroleum ether, the petroleum ether insoluble matter obtained excludes most of the saturated parts, leaving only substances mainly composed of aromatic parts and gum components. n-Butanol has a strong alkane solubility, so it has a large solubility for saturated parts mainly composed of alkanes. At the same time, it has a good solubility for hydroxyl polar components with slightly stronger polarity. Therefore, the n-butanol insoluble matter basically excludes most of the aromatic parts with slightly worse polarity and a small part of gum with lower polarity. The obtained n-butanol insoluble matter contains a small part of aromatic parts with strong polarity and most of the gum components with strong polarity. The hard carbon material obtained using this component as a precursor has a cross-linked structure with a large interlayer spacing, which is suitable as a hard carbon material for the positive electrode of sodium ion batteries.

[0033] Furthermore, in S4, the temperature is raised to 350°C to 550°C at a rate of 3°C / min to 8°C / min, and the pre-carbonization time is 0.5h to 2h.

[0034] It should be noted that the pre-carbonization was performed under an air atmosphere.

[0035] Furthermore, in S4, the temperature is raised to 750°C~1600°C at a rate of 3°C / min~8°C / min, and the high-temperature carbonization time is 2h~10h.

[0036] Pre-carbonizing and high-temperature carbonizing the precursor obtained by the tertiary extraction can eliminate unstable components in the precursor as much as possible, and is beneficial to improving the microstructure and electrochemical properties of the hard carbon material, thereby improving the overall performance of the sodium ion battery.

[0037] It should be noted that, in S4, the D50 of the hard carbon material is 5 μm to 7 μm.

[0038] Furthermore, in S4, the inert atmosphere is provided by an inert gas. The inert gas may be nitrogen, argon, helium, etc. conventional in the art. Specifically, the inert gas is introduced at a flow rate of 1 L / min to 2 L / min.

[0039] In a second aspect, the present invention further provides a hard carbon material prepared by any of the above-mentioned methods for preparing a hard carbon material.

[0040] In a third aspect, the present invention further provides a positive electrode comprising the hard carbon material.

[0041] In a fourth aspect, the present invention also provides the use of the above-mentioned hard carbon material or the above-mentioned positive electrode in the preparation of a sodium ion battery.

[0042] In a fifth aspect, the present invention also provides a sodium ion battery comprising the above-mentioned hard carbon material or the above-mentioned positive electrode.

[0043] In a sixth aspect, the present invention also provides a battery module comprising the above-mentioned sodium ion battery.

[0044] The present invention uses ethylene tar as a raw material, undergoing multi-stage extraction with an extraction solvent of a specific polarity to obtain a precursor material. This is then followed by pre-carbonization and high-temperature carbonization to obtain a hard carbon material. This, when used as a sodium ion positive electrode material, facilitates sodium ion deintercalation and rapid charge-discharge performance, and also improves the cyclic stability and overall performance of sodium ion batteries. Furthermore, ethylene tar is relatively inexpensive, and using it as a raw material to prepare the hard carbon material not only improves the overall performance of sodium ion batteries but also helps reduce their production costs. This method offers significant economic and market advantages, providing a hard carbon material with excellent overall performance for sodium ion batteries, with broad market prospects. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0046] In order to better illustrate the present invention, further examples are given below.

[0047] Example 1

[0048] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0049] Step a, weighing 300 g of ethylene tar (SP < 25° C.) and 1500 mL of quinoline into a stainless steel reactor at atmospheric pressure, heating to 80° C., stirring and extracting for 60 minutes, and filtering while hot to obtain a quinoline soluble matter; distilling the quinoline soluble matter to remove the solvent to obtain a quinoline soluble extract;

[0050] Step b, weighing 100 g of the quinoline-soluble extract and 300 mL of medium-boiling-range (60-90° C.) petroleum ether into a sealed stainless steel reactor at normal pressure, heating to 50° C., stirring and extracting for 30 minutes, and filtering while hot to obtain petroleum ether-insoluble matter;

[0051] Step c, weighing 30 g of the above petroleum ether insoluble matter and 120 mL of n-butanol, adding them to a sealed stainless steel reactor at normal pressure, heating to 60° C., stirring and extracting for 60 min, cooling to below 60° C., filtering while hot, and drying to obtain the n-butanol insoluble matter;

[0052] Step d: transfer 10 g of the above-mentioned n-butanol insoluble matter to an open tubular furnace, heat it to 360°C at a rate of 5°C / min, keep it at a constant temperature for 2 hours for pre-carbonization, then switch to a closed tubular furnace, introduce argon at a flow rate of 1.5 L / min, heat it to 1350°C at a rate of 5°C / min, keep it at this temperature for carbonization for 2 hours, cool it to room temperature, and crush it to obtain a hard carbon material with D50=6 μm.

[0053] Example 2

[0054] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0055] Step a, weighing 300 g of ethylene tar (SP < 25° C.) and 1500 mL of cyclohexanone into a stainless steel reactor at atmospheric pressure, heating to 70° C., stirring and extracting for 70 minutes, and filtering while hot to obtain a cyclohexanone-soluble matter; distilling the cyclohexanone-soluble matter to remove the solvent, to obtain a cyclohexanone-soluble extract;

[0056] Step b, weighing 100 g of the cyclohexanone-soluble extract and 300 mL of medium-boiling-range (60-90° C.) petroleum ether into a sealed stainless steel reactor at normal pressure, heating to 50° C., stirring and extracting for 30 minutes, and filtering while hot to obtain petroleum ether-insoluble matter;

[0057] Step c, weighing 30 g of the above petroleum ether insoluble matter and 110 mL of n-butanol, adding them to a sealed stainless steel reactor at normal pressure, heating to 60° C., stirring and extracting for 60 min, cooling to below 60° C., filtering while hot, and drying to obtain the n-butanol insoluble matter;

[0058] In step d, 10 g of the above-mentioned n-butanol insoluble matter was transferred to an open tubular furnace, heated to 400°C at a rate of 5°C / min, and kept at a constant temperature for 1.5 hours for pre-carbonization. Subsequently, the furnace was switched to a closed tubular furnace, argon was introduced at a flow rate of 1.5 L / min, and the temperature was increased to 1450°C at a rate of 5°C / min. The mixture was kept at this temperature for carbonization for 3 hours, cooled to room temperature, and crushed to obtain a hard carbon material with a D50 of 6 μm.

[0059] Example 3

[0060] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0061] Step a, weighing 300 g of ethylene tar (SP < 25° C.) and 1800 mL of chloroform, adding them to a stainless steel reactor at normal pressure, heating to 80° C., stirring and extracting for 60 minutes, and filtering while hot to obtain a chloroform-soluble matter; distilling the chloroform-soluble matter to remove the solvent to obtain a chloroform-soluble extract;

[0062] Step b, weighing 100 g of the chloroform-soluble extract and 200 mL of medium-boiling-range (60-90° C.) petroleum ether into a sealed stainless steel reactor at normal pressure, heating to 50° C., stirring and extracting for 30 minutes, and filtering while hot to obtain petroleum ether-insoluble matter;

[0063] Step c, weighing 30 g of the above petroleum ether insoluble matter and 90 mL of n-butanol, adding them to a sealed stainless steel reactor at normal pressure, heating to 60° C., stirring and extracting for 60 minutes, cooling to below 60° C., filtering while hot, and drying to obtain the n-butanol insoluble matter;

[0064] Step d: transfer 10 g of the above-mentioned n-butanol insoluble matter into an open tubular furnace, heat it to 500 ° C at a rate of 5 ° C / min, keep it at a constant temperature for 1 hour for pre-carbonization, then switch to a closed tubular furnace, introduce argon at a flow rate of 1.5 L / min, heat it to 1550 ° C at a rate of 6 ° C / min, keep it at this temperature for carbonization for 6 hours, cool it to room temperature, and crush it to obtain a hard carbon material with D50 = 6 μm.

[0065] Example 4

[0066] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0067] Step a, weighing 300 g of ethylene tar (SP < 25° C.) and 1600 mL of 3-pentanone into a stainless steel reactor at atmospheric pressure, heating to 90° C., stirring and extracting for 50 minutes, and filtering while hot to obtain a 3-pentanone soluble matter; distilling the 3-pentanone soluble matter to remove the solvent, to obtain a 3-pentanone soluble extract;

[0068] Step b, weighing 100 g of the above-mentioned 3-pentanone soluble extract and 400 mL of medium boiling range (60-90°C) petroleum ether, adding them to a closed stainless steel reactor at normal pressure, heating to 50°C, stirring and extracting for 30 minutes, and filtering while hot to obtain petroleum ether insoluble matter;

[0069] Step c, weighing 30 g of the above petroleum ether insoluble matter and 150 mL of isopropanol, adding them to a sealed stainless steel reactor at normal pressure, heating to 65°C, stirring and extracting for 60 minutes, cooling to below 60°C, filtering while hot, and drying to obtain the isopropanol insoluble matter;

[0070] In step d, 10 g of the above-mentioned isopropanol-insoluble material was transferred to an open tubular furnace, heated to 360°C at a rate of 5°C / min, and kept at a constant temperature for 2 hours for pre-carbonization. Subsequently, the furnace was switched to a closed tubular furnace, argon was introduced at a flow rate of 1.5 L / min, and the temperature was increased to 1200°C at a rate of 7°C / min. The mixture was kept at this temperature for carbonization for 7 hours, cooled to room temperature, and crushed to obtain a hard carbon material with a D50 of 7 μm.

[0071] Example 5

[0072] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0073] Step a, weighing 300 g of ethylene tar (SP < 25° C.) and 1200 mL of 1,1-dichloroethane into a stainless steel reactor at atmospheric pressure, heating to 85° C., stirring and extracting for 60 minutes, and filtering while hot to obtain a 1,1-dichloroethane soluble matter; distilling the 1,1-dichloroethane soluble matter to remove the solvent, to obtain a 1,1-dichloroethane soluble extract;

[0074] Step b, weighing 100 g of the above 1,1-dichloroethane soluble extract and 350 mL of medium boiling range (60-90°C) petroleum ether, adding them to a closed stainless steel reactor at normal pressure, heating to 45°C, stirring and extracting for 35 minutes, and filtering while hot to obtain petroleum ether insoluble matter;

[0075] Step c, weighing 30 g of the above petroleum ether insoluble matter and 130 mL of n-butanol, adding them to a sealed stainless steel reactor at normal pressure, heating to 70°C, stirring and extracting for 50 minutes, cooling to below 60°C, filtering while hot, and drying to obtain the n-butanol insoluble matter;

[0076] In step d, 10 g of the n-butanol insoluble material was transferred to an open tubular furnace, heated to 370°C at a rate of 5°C / min, and kept at a constant temperature for 2 hours for pre-carbonization. Subsequently, the furnace was switched to a closed tubular furnace, and argon was introduced at a flow rate of 1.5 L / min. The temperature was raised to 1400°C at a rate of 8°C / min, kept at this temperature for carbonization for 3 hours, cooled to room temperature, and crushed to obtain a hard carbon material with a D50 of 5 μm.

[0077] Example 6

[0078] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0079] Step a, weighing 300 g of ethylene tar (SP < 25° C.) and 1300 mL of quinoline into a stainless steel reactor at atmospheric pressure, heating to 75° C., stirring and extracting for 65 minutes, and filtering while hot to obtain a quinoline soluble matter; distilling the quinoline soluble matter to remove the solvent to obtain a quinoline soluble extract;

[0080] Step b, weighing 100 g of the quinoline-soluble extract and 250 mL of n-pentane, adding them to a sealed stainless steel reactor at normal pressure, heating to 55° C., stirring and extracting for 30 minutes, and filtering while hot to obtain n-pentane-insoluble matter;

[0081] Step c, weighing 30 g of the above n-pentane insoluble matter and 120 mL of amyl alcohol, adding them into a sealed stainless steel reactor at normal pressure, heating to 60° C., stirring and extracting for 60 minutes, cooling to below 60° C., filtering while hot, and drying to obtain the amyl alcohol insoluble matter;

[0082] In step d, 10 g of the above-mentioned pentanol-insoluble matter was transferred to an open tubular furnace, heated to 380°C at a rate of 7°C / min, and kept at a constant temperature for 1.5 hours for pre-carbonization. Subsequently, the furnace was switched to a closed tubular furnace, argon was introduced at a flow rate of 1.5 L / min, and the temperature was increased to 1100°C at a rate of 5°C / min. The mixture was kept at this temperature for carbonization for 4 hours, cooled to room temperature, and crushed to obtain a hard carbon material with a D50 of 6 μm.

[0083] Example 7

[0084] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0085] Step a, weighing 300 g of ethylene tar (SP < 25° C.) and 1400 mL of quinoline into a stainless steel reactor at atmospheric pressure, heating to 85° C., stirring and extracting for 55 minutes, and filtering while hot to obtain a quinoline soluble matter; distilling the quinoline soluble matter to remove the solvent to obtain a quinoline soluble extract;

[0086] Step b, weighing 100 g of the quinoline-soluble extract and 360 mL of n-octane, adding them to a sealed stainless steel reactor at normal pressure, heating to 60° C., stirring and extracting for 20 minutes, and filtering while hot to obtain n-octane-insoluble matter;

[0087] Step c, weighing 30 g of the above n-octane insoluble matter and 140 mL of n-butanol, adding them to a sealed stainless steel reactor at normal pressure, heating to 50° C., stirring and extracting for 70 minutes, cooling to below 60° C., filtering while hot, and drying to obtain the n-butanol insoluble matter;

[0088] In step d, 10 g of the above-mentioned n-butanol insoluble matter was transferred to an open tubular furnace, heated to 400°C at a rate of 5°C / min, and kept at a constant temperature for 1.5 hours for pre-carbonization. Subsequently, the furnace was switched to a closed tubular furnace, argon was introduced at a flow rate of 1.5 L / min, and the temperature was increased to 850°C at a rate of 5°C / min. The mixture was kept at this temperature for carbonization for 5 hours, cooled to room temperature, and crushed to obtain a hard carbon material with a D50 of 6 μm.

[0089] Example 8

[0090] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0091] Step a, weighing 300 g of ethylene tar (SP < 25° C.) and 1500 mL of quinoline into a stainless steel reactor at atmospheric pressure, heating to 80° C., stirring and extracting for 60 minutes, and filtering while hot to obtain a quinoline soluble matter; distilling the quinoline soluble matter to remove the solvent to obtain a quinoline soluble extract;

[0092] Step b, weighing 100 g of the quinoline-soluble extract and 320 mL of cyclohexane, adding them to a sealed stainless steel reactor at normal pressure, heating to 50° C., stirring and extracting for 30 minutes, and filtering while hot to obtain cyclohexane-insoluble matter;

[0093] Step c, weighing 30 g of the cyclohexane insoluble matter and 150 mL of isobutanol, adding them to a sealed stainless steel reactor at normal pressure, heating to 60° C., stirring and extracting for 60 min, cooling to below 60° C., filtering while hot, and drying to obtain the isobutanol insoluble matter;

[0094] In step d, 10 g of the above-mentioned isobutanol insoluble material was transferred to an open tubular furnace, heated to 350°C at a rate of 6°C / min, and kept at a constant temperature for 1 hour for pre-carbonization. Subsequently, the furnace was switched to a closed tubular furnace, argon was introduced at a flow rate of 1.5 L / min, and heated to 750°C at a rate of 5°C / min. The temperature was kept at this temperature for carbonization for 10 hours, and the temperature was cooled to room temperature and crushed to obtain a hard carbon material with a D50 of 6 μm.

[0095] Example 9

[0096] This embodiment provides a method for preparing a hard carbon material, comprising the following steps:

[0097] Step a, weighing 300 g of ethylene tar (SP < 25° C.) and 1450 mL of quinoline into a stainless steel reactor at atmospheric pressure, heating to 80° C., stirring and extracting for 60 minutes, and filtering while hot to obtain a quinoline soluble matter; distilling the quinoline soluble matter to remove the solvent to obtain a quinoline soluble extract;

[0098] Step b, weighing 100 g of the above quinoline-soluble extract and 340 mL of cyclopentane, adding them to a closed stainless steel reactor at normal pressure, heating to 40° C., stirring and extracting for 40 minutes, and filtering while hot to obtain cyclopentane-insoluble matter;

[0099] Step c, weighing 30 g of the above-mentioned cyclopentane insoluble matter and 120 mL of n-butanol, adding them to a closed stainless steel reactor at normal pressure, heating to 60° C., stirring and extracting for 60 minutes, cooling to below 60° C., filtering while hot, and drying to obtain the n-butanol insoluble matter;

[0100] In step d, 10 g of the n-butanol insoluble material was transferred to an open tubular furnace, heated to 550°C at a rate of 8°C / min, and kept at a constant temperature for 0.5 h for pre-carbonization. The furnace was then switched to a closed tubular furnace, and argon was introduced at a flow rate of 1.5 L / min. The temperature was raised to 1600°C at a rate of 5°C / min, kept at this temperature for carbonization for 2 h, cooled to room temperature, and crushed to obtain a hard carbon material with a D50 of 6 μm.

[0101] Comparative Example 1

[0102] This comparative example provides a method for preparing a hard carbon material, comprising the following steps:

[0103] Step a: Weigh 300g of ethylene tar (SP < 25°C) and place it in a high-temperature reactor. Heat it from room temperature to 200°C and keep it there for 1 hour. Then, under argon atmosphere, raise the temperature to 340°C at a rate of 1°C / min, keep it at a pressure of 0.2 MPa, and keep it there for 6 hours to obtain liquid asphalt.

[0104] Step b: transferring the liquid asphalt into a round-bottom flask, replacing the atmosphere in the round-bottom flask with air containing 60% oxygen at a gas flow rate of 40 mL / min, and maintaining the temperature at 320° C. for 2 h, cooling, filtering, and crushing to obtain a precursor;

[0105] Step c, transfer 10g of the above precursor to an open tube furnace, heat it to 360℃ at a rate of 5℃ / min, keep it at a constant temperature for 2h for pre-carbonization, then switch to a closed tube furnace, introduce argon with a flow rate of 1.5L / min, heat it to 1350℃ at a rate of 5℃ / min, keep it at this temperature for carbonization for 2h, cool it to room temperature, and crush it to obtain a hard carbon material with D50=6μm.

[0106] Comparative Example 2

[0107] This comparative example provides a method for preparing a hard carbon material. The only difference from Example 1 is that n-butanol soluble matter is selected in step c. The specific steps are as follows:

[0108] Step a, weighing 300 g of ethylene tar (SP < 25° C.) and 1500 mL of quinoline into a stainless steel reactor at atmospheric pressure, heating to 80° C., stirring and extracting for 60 minutes, and filtering while hot to obtain a quinoline soluble matter; distilling the quinoline soluble matter to remove the solvent to obtain a quinoline soluble extract;

[0109] Step b, weighing 100 g of the quinoline-soluble extract and 300 mL of medium-boiling-range (60-90° C.) petroleum ether into a sealed stainless steel reactor at normal pressure, heating to 50° C., stirring and extracting for 30 minutes, and filtering while hot to obtain petroleum ether-insoluble matter;

[0110] Step c, weighing 30 g of the petroleum ether insoluble matter and 120 mL of n-butanol into a sealed stainless steel reactor at normal pressure, heating to 60° C., stirring and extracting for 60 minutes, cooling to below 60° C., and filtering while hot to obtain n-butanol soluble matter; distilling the n-butanol soluble matter to remove the solvent to obtain an n-butanol soluble extract;

[0111] Step d: transfer 10 g of the above-mentioned n-butanol-soluble extract to an open tubular furnace, heat it to 360°C at a rate of 5°C / min, keep it at a constant temperature for 2 hours for pre-carbonization, then switch to a closed tubular furnace, introduce argon at a flow rate of 1.5 L / min, heat it to 1350°C at a rate of 5°C / min, keep it at this temperature for carbonization for 2 hours, cool it to room temperature, and crush it to obtain a hard carbon material with D50=6 μm.

[0112] Comparative Example 3

[0113] This comparative example provides a method for preparing a hard carbon material. The only difference from Example 1 is that a petroleum ether soluble substance is selected in step b. The specific steps are as follows:

[0114] Step a, weighing 300 g of ethylene tar (SP < 25° C.) and 1500 mL of quinoline into a stainless steel reactor at atmospheric pressure, heating to 80° C., stirring and extracting for 60 minutes, and filtering while hot to obtain a quinoline soluble matter; distilling the quinoline soluble matter to remove the solvent to obtain a quinoline soluble extract;

[0115] Step b, weighing 100 g of the quinoline-soluble extract and 300 mL of medium-boiling-range (60-90° C.) petroleum ether, adding the mixture to a sealed stainless steel reactor at normal pressure, heating to 50° C., stirring and extracting for 30 minutes, and filtering while hot to obtain a petroleum ether-soluble matter; removing the solvent from the petroleum ether-soluble matter to obtain a petroleum ether-soluble extract;

[0116] Step c, weighing 30 g of the petroleum ether soluble extract and 120 mL of n-butanol, adding them to a sealed stainless steel reactor at normal pressure, heating to 60° C., stirring and extracting for 60 minutes, cooling to below 60° C., filtering while hot, and drying to obtain n-butanol insoluble matter;

[0117] Step d: transfer 10 g of the above-mentioned n-butanol insoluble matter to an open tubular furnace, heat it to 360°C at a rate of 5°C / min, keep it at a constant temperature for 2 hours for pre-carbonization, then switch to a closed tubular furnace, introduce argon at a flow rate of 1.5 L / min, heat it to 1350°C at a rate of 5°C / min, keep it at this temperature for carbonization for 2 hours, cool it to room temperature, and crush it to obtain a hard carbon material with D50=6 μm.

[0118] Comparative Example 3

[0119] This comparative example provides a method for preparing a hard carbon material. The only difference between the comparative example and Example 1 is that quinoline in step a of Example 1 is substituted for an equal amount of toluene, and a toluene-soluble extract is obtained. The rest of the method is identical and will not be described again.

[0120] Comparative Example 4

[0121] This comparative example provides a method for preparing a hard carbon material. The only difference from Example 1 is that the medium-boiling petroleum ether in step b of Example 1 is replaced with an equal amount of N-methylpyrrolidone, and N-methylpyrrolidone insoluble matter is obtained. The rest is exactly the same and will not be repeated here.

[0122] Comparative Example 5

[0123] This comparative example provides a method for preparing a hard carbon material. The only difference from Example 1 is that the medium-boiling petroleum ether in step b of Example 1 is replaced with an equal amount of tetrahydrofuran, and tetrahydrofuran-insoluble matter is obtained. The rest is exactly the same and will not be repeated here.

[0124] Comparative Example 6

[0125] This comparative example provides a method for preparing a hard carbon material. The only difference between the comparative example and Example 1 is that n-butanol in step c of Example 1 is substituted for an equal amount of ethanol, and an ethanol-insoluble substance is obtained. The rest is exactly the same and will not be repeated here.

[0126] Comparative Example 7

[0127] This comparative example provides a method for preparing a hard carbon material. The only difference is that the extraction solvents in step a and step c are exchanged. The specific steps are as follows:

[0128] Step a, weighing 300 g of ethylene tar (SP < 25° C.) and 1500 mL of n-butanol into a stainless steel reactor at atmospheric pressure, heating to 80° C., stirring and extracting for 60 minutes, and filtering while hot to obtain an n-butanol-soluble matter; distilling the n-butanol-soluble matter to remove the solvent to obtain an n-butanol-soluble extract;

[0129] Step b, weighing 100 g of the n-butanol-soluble extract and 300 mL of medium-boiling-range (60-90° C.) petroleum ether into a sealed stainless steel reactor at normal pressure, heating to 50° C., stirring and extracting for 30 minutes, and filtering while hot to obtain petroleum ether-insoluble matter;

[0130] Step c, weighing 30 g of the above petroleum ether insoluble matter and 120 mL of quinoline, adding them to a sealed stainless steel reactor at normal pressure, heating to 60° C., stirring and extracting for 60 min, cooling to below 60° C., filtering while hot, and drying to obtain quinoline insoluble matter;

[0131] In step d, 10 g of the above-mentioned quinoline insoluble material was transferred to an open tubular furnace, heated to 360°C at a rate of 5°C / min, kept at a constant temperature for 2 hours for pre-carbonization, and then switched to a closed tubular furnace, and argon was introduced at a flow rate of 1.5 L / min. The temperature was raised to 1350°C at a rate of 5°C / min, kept warm for carbonization for 2 hours, cooled to room temperature, and crushed to obtain a hard carbon material with D50 = 6 μm.

[0132] Application Examples

[0133] The hard carbon materials prepared in Examples 1 to 9 and Comparative Examples 1 to 7 were assembled into sodium ion batteries for electrochemical performance testing. The specific steps are as follows:

[0134] (1) Preparation of positive electrode sheet: Hard carbon material, conductive carbon black SP, binder SBR, and binder CMC were mixed uniformly in a mass ratio of 95.5:1.5:1.5:1.5 to obtain a conductive adhesive. The conductive adhesive was evenly coated on the surface of copper foil with a scraper to a thickness of 100 mm. After drying at 100°C, the film was rolled and cut into discs with a diameter of 14 mm. The discs were weighed and set aside.

[0135] (2) Assembly of sodium ion batteries: A sodium metal sheet with a diameter of 15.8 mm and a thickness of 600 μm was used as the negative electrode, a Celgard 2400 sheet with a diameter of 16 mm and a thickness of 25 μm was used as the separator, the 14 mm positive electrode sheet prepared above was used as the working electrode, and a solution of 1 mol / L NaPF6 dissolved in dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate (volume ratio of 3:4:3) was used as the electrolyte to assemble 2032-type button cells. Five batteries were assembled for each positive electrode material, and a total of five sets of data were tested. After removing the highest and lowest data, the average of the remaining three sets of data was taken as the battery performance data.

[0136] (3) The specific test conditions for the button cell battery performance are as follows: at room temperature of 25°C, use a blue battery tester to discharge the assembled button cell at 0.1C (330mAh / g) to 0V, let it stand for 5 minutes, then discharge it at 0.02C to 0V, let it stand for another 5 minutes, and then continue to discharge it at 0.01C to 0V, ending the discharge procedure. After standing for 5 minutes, charge it at 0.1C to 2.5V. The ratio of the charge capacity to the discharge capacity is the first coulombic efficiency at 2.5V. After 2 cycles, change to 1.0CC / 1.0CD (change the current density of 0.02C to a current of 1.0C for constant current charging (CC) and constant current discharging (CD)). After 50 cycles, remove the button cell and record the capacity data, which is the cycle retention rate. The rate test is a constant 1C charge and discharge at 0.5C / 1C / 2C / 3C / 4C / 5C / 6C respectively. Each discharge rate is cycled for 5 times. The capacity data of the 1C and 6C cycles are recorded, and the 6C / 1C capacity rate retention rate can be calculated.

[0137] The results are shown in Table 1.

[0138] Table 1

[0139]

[0140] Note: 6C / 1C capacity retention rate % refers to the percentage of 6C corresponding capacity after 5 cycles / 1C corresponding capacity after 5 cycles.

[0141] The extraction yield refers to the weight of the solvent obtained from the extraction as a percentage of the mass of ethylene tar; that is, the mass percentage of the tertiary residue as a percentage of the mass of ethylene tar.

[0142] The carbonization yield refers to the mass ratio of the ethylene tar extraction component before and after carbonization at 1350°C, that is, the weight of the carbonized material / the weight of the third-stage extract after drying.

[0143] The results show that the selection of extraction solvent is crucial to the composition of the precursor, which is directly related to the extraction yield and carbonization yield of the solvent, and determines the electrochemical properties of the prepared hard carbon material.

[0144] In summary, the present invention uses lower-cost ethylene tar as a raw material, unlike most methods that use asphalt as a raw material. This eliminates the process and expense of preparing asphalt from ethylene tar. Instead, the components obtained from ethylene tar through three-stage extraction serve as hard carbon precursors, which are then directly carbonized to produce a hard carbon material. This not only eliminates the pre-oxidation steps or pre-treatment steps involving the addition of a crosslinking agent to the asphalt, but also improves the overall performance of the prepared hard carbon material. This present invention provides a low-cost, high-performance cathode material for sodium-ion batteries, which is of great significance for the development of sodium-ion batteries.

[0145] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon material, characterized in that: The steps include: S1, uniformly mixing ethylene tar and a primary extraction solvent, heating for extraction, and performing solid-liquid separation to obtain a primary extract; and removing the solvent from the primary extract to obtain a primary extract; S2, uniformly mixing the primary extract and the secondary extraction solvent, heating for extraction, and solid-liquid separation to obtain a secondary raffinate; S3, uniformly mixing the secondary raffinate and the tertiary extraction solvent, heating for extraction, cooling, solid-liquid separation, and drying to obtain a tertiary raffinate; S4, pre-carbonizing the tertiary extract at 350° C. to 550° C., then high-temperature carbonizing at 750° C. to 1600° C. under an inert atmosphere, and crushing to obtain a hard carbon material; Wherein, the primary extraction solvent includes at least one of quinoline, chloroform, 3-pentanone, 1,1-dichloroethane or cyclohexanone; the secondary extraction solvent is at least one of medium-boiling range petroleum ether, n-pentane, n-octane, cyclohexane or cyclopentane; in S3, the tertiary extraction solvent is at least one of n-butanol, isobutanol, amyl alcohol or isopropanol.

2. The method for preparing a hard carbon material according to claim 1, wherein: In S1, the temperature of the heating extraction is 70°C to 90°C, and the heating extraction time is 50min to 70min; and / or In S1, the mass volume ratio of the ethylene tar to the primary extraction solvent is 1 g:4 mL to 1 g:6 mL.

3. The method for preparing a hard carbon material according to claim 1, wherein: In S2, the mass volume ratio of the primary extract and the secondary extraction solvent is 1g:2mL~1g:4mL; and / or In S2, the temperature of the heating extraction is 40°C to 60°C, and the time of the heating extraction is 20 minutes to 40 minutes.

4. The method for preparing a hard carbon material according to claim 1, wherein: In S3, the mass volume ratio of the secondary raffinate to the tertiary extraction solvent is 1 g:3 mL to 1 g:5 mL; and / or In S3, the temperature of the heating extraction is 50° C. to 70° C., and the time of the heating extraction is 50 min to 70 min.

5. The method for preparing a hard carbon material according to claim 1, wherein: In S4, the temperature is raised to 350°C to 550°C at a rate of 3°C / min to 8°C / min, and the pre-carbonization time is 0.5h to 2h; and / or In S4, the temperature is raised to 750°C to 1600°C at a rate of 3°C / min to 8°C / min, and the high-temperature carbonization time is 2h to 10h; and / or In S4, the D50 of the hard carbon material is 5 μm to 7 μm.

6. A hard carbon material, characterized in that The hard carbon material is prepared by the method for preparing the hard carbon material according to any one of claims 1 to 5.

7. A positive electrode, characterized in that Comprising the hard carbon material according to claim 6.

8. Use of the hard carbon material according to claim 6 or the positive electrode according to claim 7 in the preparation of a sodium ion battery.

9. A sodium ion battery, characterized in that: The hard carbon material according to claim 6 or the positive electrode according to claim 7 is included.

10. A battery module, characterized in that: Including the sodium ion battery according to claim 9.

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