Coal-based hard carbon negative electrode material, preparation method thereof and sodium ion battery

Abstract

The invention relates to the technical field of sodium-ion batteries, in particular to a coal-based hard carbon negative electrode material, a preparation method thereof and a sodium-ion battery, and the preparation method comprises the following steps: mixing raw material coal powder with an organic solvent, performing solvent pretreatment, and performing solid-liquid separation, washing and drying to obtain pretreated coal powder; performing ozone oxidation treatment on the pretreated pulverized coal to obtain regulated pulverized coal; and in an inert gas atmosphere, carrying out carbonization treatment on the regulation and control pulverized coal at 1100-1700 DEG C to obtain the coal-based hard carbon negative electrode material. According to the method, the raw material coal powder is pretreated through the organic solvent to enable the raw material coal powder to expose more aromatic lamellar edges and defect sites, a large number of oxygen-containing functional groups can be efficiently introduced under mild conditions in combination with the ozone oxidation treatment process, regulation and control of the coal-based precursor structure are achieved, and the preparation process is simple. The formation of a highly disordered structure and rich closed pores in the negative electrode material can be promoted, so that the capacity and the first effect of the prepared coal-based hard carbon negative electrode material are favorably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion batteries, in particular to a coal-based hard carbon negative material, a preparation method thereof and a sodium ion battery. BACKGROUND

[0002] With the rapid growth of global electrochemical energy storage demand and the increasingly prominent problems of insufficient lithium resources, uneven distribution and rising costs, the demand for efficient, environmentally friendly and cost-controllable energy storage batteries is increasing. As a representative of low-cost secondary energy storage batteries, sodium ion batteries have ushered in an unprecedented development opportunity in recent years.

[0003] As one of the core components of sodium ion batteries, the negative material determines the key performance of the sodium ion battery, such as energy density, cycle life and rate performance. Among the many negative materials of sodium ion batteries, amorphous carbon material has become the most promising negative material due to its wide source, adjustable structure and excellent sodium storage performance. Hard carbon material in amorphous carbon is considered as the most promising negative material for sodium ion batteries due to its high reversible capacity.

[0004] Among various hard carbon material precursors, coal is an ideal raw material for preparing hard carbon material due to its high carbon content, abundant resources and low price. However, the molecular structure of coal is mainly highly condensed aromatic ring, and direct high-temperature carbonization will cause ordered rearrangement and stacking of aromatic layers, which is not conducive to the formation of highly disordered structure and rich closed pores required by hard carbon negative material, thereby resulting in low capacity and limiting its application in sodium ion batteries. SUMMARY

[0005] In order to solve the problem of low capacity of coal-based negative material prepared by directly high-temperature carbonization of coal in the prior art, the present application provides a preparation method of coal-based hard carbon negative material. The preparation method introduces an ozone oxidation step to efficiently introduce a large amount of oxygen-containing functional groups under mild conditions, and combines with a carbonization step to form highly disordered structure and rich closed pores in the negative material, thereby helping to improve the capacity of the negative material and solving the problem of low capacity of the coal-based negative material in the prior art.

[0006] The technical scheme adopted by the present application to solve its technical problems is: A preparation method of a coal-based hard carbon negative material, comprising the following steps: S1: After the raw coal powder is mixed with an organic solvent for solvent pretreatment, the pretreated coal powder is obtained after solid-liquid separation, washing and drying; S2: The pretreated coal powder is subjected to ozone oxidation treatment to obtain a regulated coal powder; S3: carbonizing the regulated coal powder at 1100-1700 DEG C under an inert gas atmosphere to obtain the coal-based hard carbon negative electrode material.

[0007] Optionally, the organic solvent is dimethyl sulfoxide.

[0008] Optionally, the ratio of the raw coal powder to the organic solvent in step S1 is 1g:(5-50)mL.

[0009] Optionally, the ozone oxidation treatment of the pretreated coal powder comprises: after the pretreated coal powder is subjected to a mixed gas with an ozone mass concentration of 3.5%-22%, the pretreated coal powder is subjected to an oxidation treatment at 25-100 DEG C.

[0010] Optionally, after the ozone oxidation treatment of the pretreated coal powder in step S2, the method further comprises: mixing the oxidized coal powder obtained by the ozone oxidation treatment with a crosslinking agent and then performing a crosslinking reaction.

[0011] Optionally, the crosslinking agent is phosphoric acid or boric acid.

[0012] Optionally, the crosslinking reaction is a microwave crosslinking reaction.

[0013] Optionally, the power of the microwave crosslinking reaction is 500-1500 W.

[0014] Another object of the present application is to provide a coal-based hard carbon negative electrode material prepared by the method for preparing the coal-based hard carbon negative electrode material as described above.

[0015] Still another object of the present application is to provide a sodium ion battery comprising the coal-based hard carbon negative electrode material as described above.

[0016] The present application has the following advantages: The method for preparing the coal-based hard carbon negative electrode material provided by the present application can promote the raw coal powder to expose more aromatic sheet edge and defect sites by pretreating the raw coal powder with an organic solvent, and then can efficiently introduce a large amount of oxygen-containing functional groups under mild conditions by combining the ozone oxidation treatment process, so as to realize the regulation of the structure of the coal-based precursor, and then can promote the formation of a highly disordered structure and rich closed pores in the negative electrode material by combining the carbonization step, thereby helping to improve the capacity of the prepared coal-based hard carbon negative electrode material. DETAILED DESCRIPTION

[0017] The present application will now be further described in detail. The examples described below are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application. Based on the examples of the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0018] Because the basic structural unit of coal, especially bituminous coal, is a planar macromolecule fused by multiple benzene rings through covalent bonds; in natural coal, these planar macromolecules tend to locally stack in an approximately parallel manner due to π-π interaction, forming 2-4 layers of "microcrystals"; this stacking is short-range, twisted, and hindered and isolated by a large number of bridges (such as methylene, ether bonds, sulfides, etc.) and side chains (such as alkyl groups, oxygen-containing functional groups, etc. connected to the edges of the planar macromolecule). If the coal is directly carbonized at high temperature, when the temperature rises to 350-450℃, the weak bridges and unstable side chains connecting the planar macromolecules begin to break, thereby destroying the original stable three-dimensional cross-linked network of the coal and "liberating" individual planar macromolecules, at this time, the system changes from a solid state to a liquid phase containing a large number of flat, freely moving planar macromolecules, which have flowability and the planar macromolecules gain degrees of freedom; once the planar macromolecules gain degrees of freedom, due to the existence of its inherent π-π conjugated system, strong electrostatic attraction occurs between the electron-rich π cloud of one planar macromolecule and the electron-deficient σ skeleton (and π cloud) of the adjacent planar macromolecule, causing these planar macromolecules to spontaneously adjust their orientation and form an ordered chain or layered structure with head-to-tail and face-to-face arrangement, obtaining a parallel stacking conformation. Driven by π-π interaction, these preliminarily arranged planar macromolecules will further merge and grow, forming a kind of liquid crystal state. When the temperature further rises to 500℃ or above, the chemical reaction changes from cracking to polycondensation, and the hydrogen atoms on the edges of the planar macromolecules are lost, exposing highly active carbon radicals. At this time, adjacent planar macromolecules will directly form strong C-C covalent bonds through these active sites, and polycondensation occurs. Finally, the "pre-assembly" liquid crystal structure guided by π-π interaction is permanently fixed and strengthened by covalent bonds. The planar macromolecules fuse into larger, layered stacked highly ordered structures, resulting in a highly ordered arrangement of carbon layers, and the resulting hard carbon has low closed porosity and poor sodium storage performance.

[0019] Based on this, the application provides a preparation method of a coal-based hard carbon negative electrode material, which comprises the following steps: S1: After the raw coal powder is mixed with an organic solvent for solvent pretreatment, solid-liquid separation, washing and drying, a pretreated coal powder is obtained; Preferably, the raw coal powder in this step is obtained by crushing the raw coal powder to Dv50 of 2-10 μm to obtain a crushed coal material; then the crushed coal material is purified using hydrochloric acid and hydrofluoric acid, or a mixed acid composed of hydrochloric acid and nitric acid, hydrofluoric acid, to obtain a purified material, which is dried to obtain the raw coal powder, wherein the purification temperature is 60-100℃; Preferably, the raw coal is selected from at least one of lean coal, lean coal, coking coal, fat coal, gas coal, weakly caking coal, non-caking coal, long flame coal and lignite; The present application realizes enrichment and homogenization of chemical components in the raw coal powder by mixing the raw coal powder with an organic solvent for pretreatment, so that more aromatic sheet layer edges and defect sites are exposed; Preferably, the solvent pretreatment in this step is carried out at 50-100 DEG C under stirring, and the stirring speed in the solvent pretreatment process is preferably 200-500 rpm, and the time of the solvent pretreatment is 3-8 h; Preferably, the solid-liquid separation method in this step is centrifugal treatment, the washing process is water washing to neutral, and the drying process is vacuum drying at 80 DEG C for 12 h; S2: ozone oxidation treatment is performed on the pretreated coal powder to obtain a regulated coal powder; In the prior art, in order to solve the problem that it is difficult to form a disordered structure and a closed pore by directly high-temperature carbonizing coal, an oxygen-containing cross-linking bond is introduced into the coal molecule through a pre-oxidation process before high-temperature carbonization, so as to effectively hinder the graphitization trend at high temperature; however, the current pre-oxidation methods such as air oxidation and nitric acid oxidation often have the problem of insufficient cross-linking degree; based on this, the present application adopts an ozone oxidation method, wherein ozone is a strong electrophilic reagent, and in the ozone oxidation treatment process, ozone first attacks the sites with high electron cloud density on the aromatic ring of coal to form unstable ozonides; the ozonides are rapidly decomposed, leading to ring-opening of the aromatic ring and generating a large number of oxygen-containing functional groups such as carboxyl (-COOH), carbonyl (C=O) and phenolic hydroxyl (-OH); this process essentially "activates" the stable sp² carbon skeleton and provides rich chemical reaction sites, so as to realize regulation of the structure of the coal-based precursor and help to improve the cross-linking degree and cross-linking efficiency; S3: carbonization treatment is performed on the regulated coal powder at 1100-1700 DEG C under an inert gas atmosphere to obtain a coal-based hard carbon negative electrode material; Preferably, in this step, the regulated coal powder is heated to 1100-1700 DEG C at a rate of 0.5-5 DEG C / min and carbonized for 1-5 h to obtain the coal-based hard carbon negative electrode material.

[0020] The preparation method of the coal-based hard carbon negative electrode material provided by the present application can promote the raw coal powder to expose more aromatic sheet layer edges and defect sites through pretreatment of the raw coal powder by an organic solvent, and can efficiently introduce a large number of oxygen-containing functional groups under mild conditions in combination with the ozone oxidation treatment process, so as to realize regulation of the structure of the coal-based precursor, and can promote the formation of a highly disordered structure and rich closed pores in the negative electrode material in combination with the carbonization step, thereby helping to improve the capacity and initial efficiency of the prepared coal-based hard carbon negative electrode material.

[0021] The organic solvent in the step S1 is preferably dimethyl sulfoxide (DMSO), which is a strong polar aprotic solvent, can effectively destroy the non-covalent interactions such as hydrogen bonds and pi-pi stacking between macromolecules in the coal, and selectively dissolve the inert components with low molecular weight and regular structure in the coal, so as to realize the enrichment and homogenization of chemical components, expose more aromatic sheet edges and defect sites, and facilitate the subsequent ozone oxidation process.

[0022] The raw coal powder and the organic solvent are preferably used in a ratio of 1g:(5-50) mL in the step S1.

[0023] The ozone oxidation treatment of the pretreated coal powder preferably comprises: after the pretreated coal powder is introduced into the mixed gas with an ozone mass concentration of 3.5%-22%, the oxidation treatment is performed at 25-100 DEG C.

[0024] Specifically, the step can be performed in a box furnace, a rotary furnace or other equipment capable of heating and constant temperature and capable of introducing an atmosphere, and the remaining gas components in the mixed gas are preferably nitrogen or nitrogen-oxygen mixed gas or nitrogen-oxygen-argon mixed gas, and the oxidation time is preferably 1-8h; defects and micropore structures are introduced on the particle surface through the oxidation reaction, more active sites are constructed, which is beneficial to the embedding and extraction of sodium ions and improves the specific capacity of the material.

[0025] To further improve the crosslinking degree, the step S2 preferably further comprises: after the pretreated coal powder is subjected to the ozone oxidation treatment, the oxidized coal powder obtained by the ozone oxidation treatment is mixed with a crosslinking agent to perform a crosslinking reaction, and in the process, the crosslinking agent reacts with the oxygen-containing functional groups in the oxidized coal powder to realize rapid, uniform and deep crosslinking.

[0026] By performing the crosslinking reaction before high-temperature carbonization, a covalent crosslinking network with high thermal stability can be actively constructed in the precursor, so that the structure of the coal-based precursor can be more accurately regulated, and the ordering of the coal-based precursor can be effectively prevented in the carbonization process, so that a hard carbon negative electrode material rich in ultramicropores, thin pore walls and good connectivity can be accurately created.

[0027] The crosslinking agent is preferably phosphoric acid or boric acid.

[0028] When the phosphoric acid is used as the crosslinking agent, the hydroxyl groups of the phosphoric acid and the carboxyl groups and phenolic hydroxyl groups on the coal molecules undergo esterification and dehydration reaction to form a C-O-P-O-C covalent crosslinking bridge with high thermal stability; the phosphoric acid also acts as an acid catalyst to accelerate the process.

[0029] When boric acid is used as the crosslinking agent, the boric acid and the ortho-diol structure generated by ozone oxidation on the coal molecules undergo cyclization esterification reaction to form stable five-membered or six-membered ring boric acid ester (B-O-C) structure, which tightly connects different coal molecular chains to form a covalent crosslinking network.

[0030] The P-O-C or B-O-C covalent crosslinking network formed in the process acts as a rigid "scaffold" in the carbonization process, effectively hinders the planar growth and ordered stacking of aromatic sheets, thereby preventing the ordering thereof, and generates a hard carbon material with rich closed pores, thin pore walls and good connectivity, which can exhibit high capacity and high initial efficiency as a negative electrode material of a sodium ion battery, and the process route is clear, and has good industrialization prospect.

[0031] The mass ratio of the crosslinking agent to the oxidized coal powder is preferably (0.2-0.4):1.

[0032] The present application further preferably uses microwave crosslinking reaction to utilize the bulk heating and hot spot effect of microwaves to make the crosslinking agent and oxygen-containing functional group molecules vibrate at high speed, so that the reaction temperature is reached instantaneously, the activation energy of the reaction is greatly reduced, the crosslinking reaction is completed within a few minutes, and the uniformity is far superior to that of traditional heating.

[0033] The power of the microwave crosslinking reaction is preferably 500-1500 W, and the reaction time is 10-20 min.

[0034] The microwave crosslinking reaction can be carried out in air or inert gas atmosphere.

[0035] The present application realizes precise regulation of the structure of the coal-based precursor through the three-step synergistic strategy of DMSO pretreatment to enrich active components, ozone oxidation to implant functional groups and microwave-assisted chemical crosslinking to construct a stable network; and the material obtained through the preparation method has a highly disordered amorphous structure, and the enclosed space forms closed ultramicro-pores for sodium storage.

[0036] Compared with the prior art, the preparation method provided by the present application simplifies the process flow, greatly accelerates the crosslinking reaction rate by utilizing the bulk heating and "hot spot" effect of microwaves, and ensures that the crosslinking network is uniformly formed in the bulk phase of the coal powder, overcoming the temperature gradient problem of traditional heating; phosphoric acid or boric acid is used as the crosslinking agent to form a covalent bond with the oxygen-containing functional groups, the network has high thermal stability and can effectively inhibit graphitization in the high-temperature carbonization process. The obtained coal-based hard carbon negative electrode material has rich ultramicro-pores, ultrathin pore walls and a highly disordered carbon layer structure, and exhibits high reversible specific capacity and high initial coulombic efficiency as a negative electrode of a sodium ion battery. The preparation method is suitable for various coal types, and ozone has no residual pollution, and has broad industrial application prospect.

[0037] Another object of the present application is to provide a coal-based hard carbon negative electrode material prepared by the preparation method of the coal-based hard carbon negative electrode material as described above.

[0038] The coal-based hard carbon negative electrode material provided by the present application can efficiently introduce a large number of oxygen-containing functional groups under mild conditions by pretreating the raw coal powder with an organic solvent to expose more aromatic sheet edge and defect sites, in combination with an ozone oxidation process, so as to realize the regulation of the structure of the coal-based precursor, in combination with a carbonization step, so as to promote the formation of highly disordered structures and rich closed pores in the formed negative electrode material, thereby helping to improve the capacity of the coal-based hard carbon negative electrode material.

[0039] Another object of the present application is to provide a sodium ion battery comprising the coal-based hard carbon negative electrode material as described above.

[0040] The sodium ion battery provided by the present application adopts the coal-based hard carbon negative electrode material, the preparation process of which can efficiently introduce a large number of oxygen-containing functional groups under mild conditions by pretreating the raw coal powder with an organic solvent to expose more aromatic sheet edge and defect sites, in combination with an ozone oxidation process, so as to realize the regulation of the structure of the coal-based precursor, in combination with a carbonization step, so as to promote the formation of highly disordered structures and rich closed pores in the formed negative electrode material, thereby helping to improve the capacity and initial efficiency.

[0041] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below.

[0042] Example 1 The present embodiment provides a preparation method of a coal-based hard carbon negative electrode material, which comprises the following steps: S1: 20 g of bituminous coal is pulverized to Dv50 of 6 μm, and then treated with 2 mol / L hydrochloric acid and 20% hydrofluoric acid at 60°C for 12 hours respectively, and then filtered, washed with deionized water until neutral, and then vacuum dried at 80°C for 12 hours to obtain raw coal powder; 10 g of the raw coal powder is placed in a flask with 200 mL of DMSO, and stirred at 300 rpm in an 80°C oil bath for 6 hours, and then centrifuged at a speed of 8000 rpm for 10 minutes, and then the precipitate is washed with deionized water until neutral, and then vacuum dried at 80°C for 12 hours to obtain pretreated coal powder; S2: The pretreated coal powder is placed in a quartz boat and put into a rotary furnace, and then ozone / nitrogen mixed gas with an ozone mass concentration of 12% (total flow rate of 150 L / h) is introduced, and then oxidized at 80°C for 5 hours to obtain oxidized coal powder; Take 5 g of oxidized coal powder, mix with 1.5 g of boric acid dissolved in 10 mL of hot deionized water, ultrasonic dispersion and mechanical stirring for 2 hours, and then pre-dry at 80℃; the dried sample is transferred into a microwave reactor, reacted at 800 W power for 15 minutes, and after natural cooling, the regulated coal powder is obtained; S3: Put the regulated coal powder into a tube furnace, heat to 1300℃ at a rate of 2℃ / min under nitrogen atmosphere, keep for 2 hours, and cool to room temperature with the furnace, to obtain a coal-based hard carbon negative electrode material.

[0043] Example 2 The present embodiment provides a preparation method of a coal-based hard carbon negative electrode material, which comprises the following steps: S1: Take 20 g of bituminous coal, crush to Dv50 of 6 μm, and then sequentially stir with 2 mol / L hydrochloric acid and 20% hydrofluoric acid at 60℃ for 12 hours respectively, filter, wash with deionized water until neutral, and then vacuum dry at 80℃ for 12 hours to obtain raw coal powder; Put 10 g of raw coal powder and 200 mL of DMSO into a flask, stir at 300 rpm in an 80℃ oil bath for 6 hours, then centrifuge at 8000 rpm for 10 minutes, take the precipitate, wash with deionized water until neutral, and then vacuum dry at 80℃ for 12 hours to obtain pretreated coal powder; S2: Put the pretreated coal powder into a quartz boat and put it into a rotary furnace, and then pass in ozone / nitrogen mixed gas with an ozone mass concentration of 12% (total flow rate 150 L / h), and oxidize at 80℃ for 5 hours to obtain oxidized coal powder; Take 5 g of oxidized coal powder, mix with 1.5 g of 85% phosphoric acid and 5 mL of deionized water, ultrasonic dispersion and mechanical stirring for 2 hours, and then pre-dry at 80℃; the dried sample is transferred into a microwave reactor, reacted at 800 W power for 15 minutes, and after natural cooling, the regulated coal powder is obtained; S3: Put the regulated coal powder into a tube furnace, heat to 1300℃ at a rate of 2℃ / min under nitrogen atmosphere, keep for 2 hours, and cool to room temperature with the furnace, to obtain a coal-based hard carbon negative electrode material.

[0044] Example 3 The present embodiment provides a preparation method of a coal-based hard carbon negative electrode material, which comprises the following steps: S1: Take 20 g of bituminous coal, crush to Dv50 of 6 μm, and then sequentially stir with 2 mol / L hydrochloric acid and 20% hydrofluoric acid at 60℃ for 12 hours respectively, filter, wash with deionized water until neutral, and then vacuum dry at 80℃ for 12 hours to obtain raw coal powder; 10 g of the raw coal powder was placed in a flask with 200 mL of DMSO, stirred at 300 rpm in an 80°C oil bath for 6 hours, then centrifuged at 8000 rpm for 10 minutes, the precipitate was taken, washed with deionized water until neutral, vacuum dried at 80°C for 12 hours, and the pretreated coal powder was obtained; S2: The pretreated coal powder was placed in a quartz boat and put into a tube furnace, and ozone / nitrogen mixed gas with an ozone mass concentration of 3.5% (total flow rate 150 L / h) was introduced, and the oxidation treatment was carried out at 100°C for 8 hours to obtain the oxidized coal powder; 5 g of the oxidized coal powder was mixed with a solution prepared by 1.5 g of 85% phosphoric acid and 5 mL of deionized water, ultrasonic dispersed and mechanically stirred for 2 hours, and then pre-dried at 80°C; the dried sample was transferred into a microwave reactor, reacted at 800 W power for 15 minutes, and the regulated coal powder was obtained after natural cooling; S3: The regulated coal powder was placed in a tube furnace, heated to 1300°C at a rate of 2°C / min under a nitrogen atmosphere, kept for 2 hours, and cooled to room temperature with the furnace, to obtain the coal-based hard carbon negative electrode material.

[0045] Example 4 The present embodiment provides a preparation method of a coal-based hard carbon negative electrode material, which comprises the following steps: S1: 20 g of bituminous coal was crushed to Dv50 of 6 μm, and then stirred at 60°C for 12 hours with 2 mol / L hydrochloric acid and 20% hydrofluoric acid respectively, filtered, washed with deionized water until neutral, and vacuum dried at 80°C for 12 hours to obtain the raw coal powder; 10 g of the raw coal powder was placed in a flask with 200 mL of DMSO, stirred at 300 rpm in an 80°C oil bath for 6 hours, then centrifuged at 8000 rpm for 10 minutes, the precipitate was taken, washed with deionized water until neutral, vacuum dried at 80°C for 12 hours, and the pretreated coal powder was obtained; S2: The pretreated coal powder was placed in a quartz boat and put into a tube furnace, and ozone / nitrogen mixed gas with an ozone mass concentration of 3.5% (total flow rate 150 L / h) was introduced, and the oxidation treatment was carried out at 100°C for 8 hours to obtain the oxidized coal powder; 5 g of the oxidized coal powder was mixed with a solution prepared by 1.5 g of 85% phosphoric acid and 5 mL of deionized water, ultrasonic dispersed and mechanically stirred for 2 hours, and then pre-dried at 80°C; the dried sample was transferred into a microwave reactor, reacted at 800 W power for 15 minutes, and the regulated coal powder was obtained after natural cooling; S3: The regulated coal powder was placed in a tube furnace, heated to 1300°C at a rate of 2°C / min under a nitrogen atmosphere, kept for 2 hours, and cooled to room temperature with the furnace, to obtain the coal-based hard carbon negative electrode material.

[0046] Example 5 The embodiment provides a preparation method of a coal-based hard carbon negative material, and the preparation method comprises the following steps: S1: 20 g of bituminous coal is crushed to Dv50 of 6 μm, and then sequentially stirred with 2 mol / L hydrochloric acid and 20% hydrofluoric acid at 60°C for 12 hours; the mixture is filtered, washed with deionized water until neutral, and then vacuum dried at 80°C for 12 hours to obtain raw coal powder; 10 g of the raw coal powder is placed in a flask with 200 mL of DMSO, stirred at 300 rpm in an 80°C oil bath for 6 hours, and then centrifuged at a speed of 8000 rpm for 10 minutes; the precipitate is washed with deionized water until neutral, and then vacuum dried at 80°C for 12 hours to obtain pretreated coal powder; S2: the pretreated coal powder is placed in a quartz boat and put into a rotary furnace, and ozone / nitrogen mixed gas with an ozone mass concentration of 12% (total flow rate of 150 L / h) is introduced to oxidize the pretreated coal powder at 80°C for 5 hours to obtain oxidized coal powder; 5 g of the oxidized coal powder is mixed with a solution prepared by mixing 1.0 g of 85% phosphoric acid and 5 mL of deionized water, ultrasonically dispersed and mechanically stirred for 2 hours, and then pre-dried at 80°C; the dried sample is transferred into a microwave reactor and reacted at a power of 500 W for 15 minutes to obtain regulated coal powder after natural cooling; S3: the regulated coal powder is placed in a tube furnace, heated to 1300°C at a rate of 2°C / min under a nitrogen atmosphere, kept for 2 hours, and then cooled to room temperature with the furnace to obtain a coal-based hard carbon negative material.

[0047] Example 6 The embodiment provides a preparation method of a coal-based hard carbon negative material, and the preparation method comprises the following steps: S1: 20 g of bituminous coal is crushed to Dv50 of 6 μm, and then sequentially stirred with 2 mol / L hydrochloric acid and 20% hydrofluoric acid at 60°C for 12 hours; the mixture is filtered, washed with deionized water until neutral, and then vacuum dried at 80°C for 12 hours to obtain raw coal powder; 10 g of the raw coal powder is placed in a flask with 200 mL of DMSO, stirred at 300 rpm in an 80°C oil bath for 6 hours, and then centrifuged at a speed of 8000 rpm for 10 minutes; the precipitate is washed with deionized water until neutral, and then vacuum dried at 80°C for 12 hours to obtain pretreated coal powder; S2: the pretreated coal powder is placed in a quartz boat and put into a rotary furnace, and ozone / nitrogen mixed gas with an ozone mass concentration of 12% (total flow rate of 150 L / h) is introduced to oxidize the pretreated coal powder at 80°C for 5 hours to obtain oxidized coal powder; Take 5 g of oxidized coal powder, mix with a solution prepared from 2.0 g of 85% phosphoric acid and 5 mL of deionized water, ultrasonic dispersion and mechanical stirring for 2 hours, and then pre-drying at 80°C; the dried sample is transferred into a microwave reactor, reacted at 1500 W power for 10 minutes, and after natural cooling, the regulated coal powder is obtained; S3: The regulated coal powder is placed in a tube furnace, heated to 1300°C at a rate of 2°C / min under a nitrogen atmosphere, and kept for 2 hours, and then cooled to room temperature with the furnace, to obtain a coal-based hard carbon negative electrode material.

[0048] Example 7 The present example provides a preparation method of a coal-based hard carbon negative electrode material, which comprises the following steps: S1: Take 20 g of bituminous coal, crush to Dv50 of 6 μm, and then sequentially stir at 60°C for 12 hours with 2 mol / L hydrochloric acid and 20% hydrofluoric acid, respectively, filter, wash with deionized water until neutral, and then vacuum dry at 80°C for 12 hours to obtain raw coal powder; Put 10 g of raw coal powder and 200 mL of DMSO into a flask, stir at 300 rpm in an 80°C oil bath for 6 hours, and then centrifuge at 8000 rpm for 10 minutes, take the precipitate, wash with deionized water until neutral, and then vacuum dry at 80°C for 12 hours to obtain pretreated coal powder; S2: Put the pretreated coal powder into a quartz boat and place it in a rotary furnace, and then pass in ozone / nitrogen mixed gas with an ozone mass concentration of 12% (total flow rate of 150 L / h), and oxidize at 80°C for 5 hours to obtain oxidized coal powder; Take 5 g of oxidized coal powder, mix with a solution prepared from 2.0 g of 85% phosphoric acid and 5 mL of deionized water, ultrasonic dispersion and mechanical stirring for 2 hours, and then pre-drying at 80°C; the dried sample is transferred into a microwave reactor, reacted at 1500 W power for 10 minutes, and after natural cooling, the regulated coal powder is obtained; S3: The regulated coal powder is placed in a tube furnace, heated to 1300°C at a rate of 2°C / min under a nitrogen atmosphere, and kept for 2 hours, and then cooled to room temperature with the furnace, to obtain a coal-based hard carbon negative electrode material.

[0049] Example 8 The present example provides a preparation method of a coal-based hard carbon negative electrode material, which comprises the following steps: S1: Take 20 g of bituminous coal, crush to Dv50 of 6 μm, and then sequentially stir at 60°C for 12 hours with 2 mol / L hydrochloric acid and 20% hydrofluoric acid, respectively, filter, wash with deionized water until neutral, and then vacuum dry at 80°C for 12 hours to obtain raw coal powder; 10 g of raw coal powder was placed in a flask with 200 mL of DMSO, stirred at 300 rpm in an 80°C oil bath for 6 hours, then centrifuged at a speed of 8000 rpm for 10 minutes, the precipitate was washed with deionized water until neutral, and vacuum dried at 80°C for 12 hours to obtain the pretreated coal powder; S2: The pretreated coal powder was placed in a quartz boat and put into a rotary furnace, and ozone / nitrogen mixed gas with an ozone mass concentration of 12% (total flow rate 150 L / h) was introduced, and the oxidation treatment was carried out at 80°C for 5 hours to obtain the regulated coal powder; S3: The regulated coal powder was placed in a tube furnace, heated to 1300°C at a rate of 2°C / min under a nitrogen atmosphere, and held for 2 hours, then cooled to room temperature with the furnace to obtain the coal-based hard carbon negative electrode material.

[0050] Comparative Example 1 The present comparative example provides a preparation method of a coal-based hard carbon negative electrode material, which comprises the following steps: S1: 20 g of bituminous coal was crushed to a Dv50 of 6 μm, and then sequentially treated with 2 mol / L hydrochloric acid and 20% hydrofluoric acid at 60°C for 12 hours each, filtered, washed with deionized water until neutral, and vacuum dried at 80°C for 12 hours to obtain the raw coal powder; S2: 10 g of the raw coal powder was placed in a quartz boat and put into a rotary furnace, and ozone / nitrogen mixed gas with an ozone mass concentration of 12% (total flow rate 150 L / h) was introduced, and the oxidation treatment was carried out at 80°C for 5 hours to obtain the oxidized coal powder; 5 g of the oxidized coal powder was mixed with a solution of 1.5 g of 85% phosphoric acid and 5 mL of deionized water, ultrasonically dispersed and mechanically stirred for 2 hours, and then pre-dried at 80°C; the dried sample was transferred into a microwave reactor and reacted at a power of 800 W for 15 minutes, and then naturally cooled to obtain the regulated coal powder; S3: The regulated coal powder was placed in a tube furnace, heated to 1300°C at a rate of 2°C / min under a nitrogen atmosphere, and held for 2 hours, then cooled to room temperature with the furnace to obtain the coal-based hard carbon negative electrode material.

[0051] Comparative Example 2 The present example provides a preparation method of a coal-based hard carbon negative electrode material, which comprises the following steps: S1: 20 g of bituminous coal was crushed to a Dv50 of 6 μm, and then sequentially treated with 2 mol / L hydrochloric acid and 20% hydrofluoric acid at 60°C for 12 hours each, filtered, washed with deionized water until neutral, and vacuum dried at 80°C for 12 hours to obtain the raw coal powder; 10 g of raw coal powder was placed in a flask with 200 mL of DMSO, stirred at 300 rpm in an 80℃ oil bath for 6 hours, then centrifuged at a speed of 8000 rpm for 10 minutes, the precipitate was washed with deionized water until neutral, and dried at 80℃ under vacuum for 12 hours to obtain the pretreated coal powder; S2: The pretreated coal powder was placed in a quartz boat and put into a tube furnace, and was oxidized at 300℃ for 5 hours in an air atmosphere to obtain the oxidized coal powder; 5 g of the oxidized coal powder was mixed with a solution prepared by mixing 1.5 g of 85% phosphoric acid and 5 mL of deionized water, ultrasonic dispersed and mechanically stirred for 2 hours, and then pre-dried at 80℃; the dried sample was transferred into a microwave reactor and reacted at a power of 800 W for 15 minutes, and the regulated coal powder was obtained after natural cooling; S3: The regulated coal powder was placed in a tube furnace, heated to 1300℃ at a rate of 2℃ / min in a nitrogen atmosphere, kept for 2 hours, and cooled to room temperature with the furnace, to obtain the coal-based hard carbon negative electrode material.

[0052] Comparative Example 3 The present comparative example provides a preparation method of a coal-based hard carbon negative electrode material, which comprises the following steps: S1: 20 g of bituminous coal was crushed to a Dv50 of 6 μm, and was stirred at 60℃ for 12 hours with 2 mol / L hydrochloric acid and 20% hydrofluoric acid by mass respectively, and then was filtered, washed with deionized water until neutral, and dried at 80℃ under vacuum for 12 hours to obtain the raw coal powder; S2: The raw coal powder was placed in a tube furnace, heated to 1300℃ at a rate of 2℃ / min in a nitrogen atmosphere, kept for 2 hours, and cooled to room temperature with the furnace, to obtain the coal-based hard carbon negative electrode material.

[0053] The performance of the coal-based hard carbon negative electrode material prepared in each of the above examples and comparative examples was tested.

[0054] The performance of the coal-based hard carbon negative electrode material prepared in each of the above examples and comparative examples was evaluated by a button cell. The mass ratio of the electrode slurry was active material (coal-based hard carbon negative electrode material): conductive agent (carbon black): binder (polyvinylidene fluoride) = 90:5:5, and an appropriate amount of N-methyl pyrrolidone was added to prepare a slurry. The slurry was coated on a copper foil with a coating thickness of 100 μm, and was dried and pressed to form an electrode sheet. A 2032 button cell was assembled with the electrode sheet as the anode, metal sodium as the cathode, a solution of NaPF6 in DEC+EC (volume ratio 1:1) as the electrolyte, and glass fiber GF / C as the separator. The test results are shown in Table 1. -1 NaPF6 in DEC+EC (volume ratio 1:1) as the electrolyte, and glass fiber GF / C as the separator. The test results are shown in Table 1.

[0055] Table 1 From the data in the above table, it can be seen that the coal-based hard carbon negative electrode materials prepared by each embodiment of the present application all have excellent reversible specific capacity and initial efficiency. Moreover, comparing the test data of Example 7 and Example 8 with Example 2, it can be seen that the electrochemical performance of the negative electrode material prepared after microwave crosslinking reaction is significantly better than that of the negative electrode material without microwave crosslinking and the negative electrode material prepared by traditional heating crosslinking.

[0056] Comparative Example 1, compared with Example 2, was not pretreated with an organic solvent before ozone oxidation, so although the ozone oxidation and microwave crosslinking process were used, the capacity was lower due to the reduction of the introduced oxygen-containing functional groups compared with Example 2.

[0057] Comparative Example 2, compared with Example 2, used oxygen oxidation instead of ozone oxidation, because the oxygen oxidation process directly attacks the weak bridge bonds and unstable side chains connecting the planar macromolecules in the coal, and cannot achieve ring opening, resulting in insufficient crosslinking and low capacity.

[0058] Comparative Example 3 directly carbonized the raw coal powder at high temperature, and because it was difficult to form a disordered structure and closed pores, the capacity was low.

[0059] Based on the above ideal embodiments according to the present application, through the above description, relevant personnel can certainly make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims

1. A method for preparing a coal-based hard carbon anode material, characterized in that, The method comprises the following steps: S1: mixing raw coal powder with organic solvent for solvent pretreatment, then performing solid-liquid separation, washing and drying to obtain pretreated coal powder; S2: performing ozone oxidation treatment on the pretreated coal powder to obtain regulated coal powder; S3: performing carbonization treatment on the regulated coal powder at 1100-1700 ℃ under inert gas atmosphere to obtain coal-based hard carbon negative electrode material.

2. The preparation method of the coal-based hard carbon anode material as described in claim 1, characterized in that, The organic solvent is dimethyl sulfoxide.

3. The preparation method of the coal-based hard carbon anode material as described in claim 1, characterized in that, The ratio of the raw coal powder to the organic solvent in step S1 is 1 g: (5-50) mL.

4. The preparation method of the coal-based hard carbon anode material as described in claim 1, characterized in that, The ozone oxidation treatment on the pretreated coal powder comprises: introducing mixed gas with ozone mass concentration of 3.5%-22% into the pretreated coal powder, and then performing oxidation treatment at 25-100 ℃.

5. The method of producing a coal-based hard carbon anode material according to any one of claims 1 to 4, wherein After the ozone oxidation treatment on the pretreated coal powder in step S2, the method further comprises: mixing the oxidized coal powder obtained by the ozone oxidation treatment with a crosslinking agent, and then performing crosslinking reaction.

6. The method for preparing the coal-based hard carbon anode material as described in claim 5, characterized in that, The crosslinking agent is phosphoric acid or boric acid.

7. The method for preparing the coal-based hard carbon anode material as described in claim 5, characterized in that, The crosslinking reaction is microwave crosslinking reaction.

8. The method for preparing the coal-based hard carbon anode material as described in claim 7, characterized in that, The power of the microwave crosslinking reaction is 500-1500 W.

9. A coal-based hard carbon anode material, characterized in that, The coal-based hard carbon negative electrode material is prepared by the method according to any one of claims 1-8.

10. A sodium-ion battery, characterized in that, The coal-based hard carbon negative electrode material according to claim 9.

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