Coal-based hard carbon negative electrode material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of coal-based hard carbon negative electrode materials, discloses a coal-based hard carbon negative electrode material as well as a preparation method and application thereof, and solves the problems of relatively low specific capacity and initial coulombic efficiency of the coal-based hard carbon negative electrode material. The preparation method of the coal-based hard carbon negative electrode material comprises the following steps: S1, activating pulverized coal to obtain activated pulverized coal; s2, mixing the activated pulverized coal with nanoscale thermoplastic resin to obtain a mixture, and performing pre-carbonization treatment on the mixture; and S3, performing carbonization treatment on the product in the S2 to obtain the coal-based hard carbon negative electrode material. The pre-carbonization treatment comprises the following steps: putting the mixture into a mold, filling nitrogen into the mold for the first time, heating to a first target temperature, and preserving heat; carrying out first vacuum exhaust and step-by-step mold pressing; and after step-by-step mold pressing is completed, the temperature is increased to a second target temperature, heat preservation is conducted, and then nitrogen is charged for the second time. The specific capacity and the first coulombic efficiency of the prepared coal-based hard carbon negative electrode material are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of coal-based hard carbon anode materials, specifically to a coal-based hard carbon anode material, its preparation method, and its applications. Background Technology

[0002] Compared to lithium-ion batteries, sodium-ion batteries offer superior safety and better low-temperature performance, making them promising for large-scale energy storage applications where energy density is not a primary factor. Currently, the industry generally believes that the key to commercializing sodium-ion batteries lies in the anode material. Therefore, developing high-performance, low-cost hard carbon anode materials is a crucial task. Coal, as a traditional energy source with abundant reserves and diverse varieties, possesses numerous advantages such as moderate molecular weight and easily controllable molecular structure, and its application in sodium-ion batteries is relatively low-cost, making it a potential precursor for hard carbon anodes in sodium storage. However, coal generates numerous surface defects during pyrolysis, resulting in low specific capacity and unsatisfactory initial coulombic efficiency, limiting its application in high-energy-density batteries.

[0003] One existing approach is to improve the performance of coal-based hard carbon by doping it with heteroatoms, but this process is costly and complex. Another approach is to adjust the pore distribution of coal-based hard carbon through activation, which improves the specific capacity and initial coulombic efficiency of the product to some extent, but the improvement effect is not significant.

[0004] Therefore, there is an urgent need to develop a low-cost, simple, and effective method for preparing coal-based hard carbon that can improve specific capacity and initial coulombic efficiency. Summary of the Invention

[0005] This invention provides a coal-based hard carbon anode material, its preparation method, and its applications, in order to solve the problems of low specific capacity and initial coulombic efficiency of existing coal-based hard carbon anode materials.

[0006] In a first aspect, the present invention provides a method for preparing a coal-based hard carbon anode material, comprising the following steps: S1. Activate the coal powder to obtain activated coal powder; S2. The activated coal powder is mixed with nano-scale thermoplastic resin to obtain a mixture, and the mixture is subjected to pre-carbonization treatment; S3. The product of S2 is subjected to carbonization treatment to obtain the coal-based hard carbon anode material. In step S2, the pre-carbonization process includes: placing the mixture into a mold, filling the mold with nitrogen for the first time, heating to a first target temperature and holding it at that temperature; then performing a first vacuum degassing and step-by-step molding; after the step-by-step molding is completed, heating to a second target temperature and holding it at that temperature, and then filling with nitrogen for the second time. The first target temperature is above the melting point of the nanoscale thermoplastic resin; The stepwise molding process includes: first pressurizing to 0.2MPa~1MPa and holding for 10~15min; then increasing the pressure by 2~5MPa each time, and holding for 10~15min after each pressurization, until the pressure rises to 15~18MPa; The second target temperature is 200~600℃.

[0007] In one possible implementation, the molding equipment used is a high-temperature molding machine and its matching mold.

[0008] The mold material is one or more of H13 mold steel, H11 mold steel, and 5CrNiMo mold steel.

[0009] The first target temperature melts the nano-sized thermoplastic resin, and the second target temperature pre-carbonizes the nano-sized thermoplastic resin and activated coal powder. The step-by-step molding is performed while maintaining the first target temperature. Nitrogen gas is first introduced into the mold to maintain a nitrogen atmosphere. During the heating to and holding at the second target temperature, the pressure applied at the end of the step-by-step molding is maintained. A first vacuum venting removes the atmosphere from the material's pores, and a second nitrogen introduction after heating to and holding at the second target temperature prevents oxidation or even combustion of the material.

[0010] In one possible implementation, nitrogen gas is first introduced into the mold to a slightly positive pressure, for example, 0.001 to 0.005 bar (gauge pressure).

[0011] In one possible implementation, nitrogen is introduced a second time to a slightly positive pressure, for example, 0.001 to 0.005 bar (gauge pressure).

[0012] In one possible implementation, the step of first filling the mold with nitrogen gas includes: filling with nitrogen gas → second vacuum exhaust → filling with nitrogen gas; The nitrogen filling rate is 100~500ml / min; The exhaust speed of the second vacuum exhaust is 100~500ml / min; In one possible implementation, the rate of nitrogen filling for the second time is 100-500 ml / min; In one possible implementation, the exhaust rate of the first vacuum exhaust is 100~500 ml / min.

[0013] Controlling the nitrogen charging rate and venting speed can prevent uneven material distribution in the mold.

[0014] In one possible implementation, the first target temperature is 10-20°C above the melting point of the nanoscale thermoplastic resin; In one possible implementation, the holding time for heating to the first target temperature and holding it at that temperature is 2 to 8 hours. In one possible implementation, the heating rate to the first target temperature is 15~20℃ / min; In one possible implementation, the holding time for heating to the second target temperature and holding it at that temperature is 1 to 10 hours. In one possible implementation, the heating rate to the second target temperature is 3~6℃ / min; In one possible implementation, the second target temperature is 300~500°C.

[0015] In one possible implementation, the mass ratio of the activated coal powder to the nanoscale thermoplastic resin is (6~10):1; In one possible implementation, the particle size of the nanoscale thermoplastic resin is 10~300nm, preferably 20~100nm; In one possible implementation, the nanoscale thermoplastic resin includes one or more of polycaprolactone (PCL), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), and polyethylene terephthalate (PET).

[0016] In one possible implementation, the coal powder particle size Dv50 is 3~30μm, preferably 3~15μm; In one possible implementation, the pulverized coal is obtained by crushing coal, and the coal is selected from one or more of bituminous coal, sub-bituminous coal, and anthracite; Optionally, the pulverized coal is obtained through coal crushing, acid washing, water washing, and drying; Optionally, the acid used for pickling is one or more of hydrochloric acid, hydrofluoric acid, and nitric acid; Optionally, the pickling temperature is 40~70℃, and the time is 0.5~24h; Optionally, the drying temperature is 105-120℃ and the drying time is 5-24h.

[0017] In one possible implementation, in step S1, steam is used to activate the pulverized coal. Optionally, the activation temperature is 450~900℃, preferably 600~800℃; Optionally, the activation time is 2-6 hours, preferably 3-5 hours; Optionally, the equipment used for activation may be one or more of the following: tube furnace, box furnace, and rotary furnace.

[0018] In one possible implementation, the carbonization temperature is 800~1600℃, preferably 1000~1400℃; In one possible implementation, the carbonization treatment time is 0.5 to 6 hours, preferably 2 to 4 hours; In one possible implementation, the heating rate to the carbonization treatment temperature is 1~20℃ / min, preferably 1~10℃ / min.

[0019] In one possible implementation, in S3, before carbonizing the product of S2, the product of S2 is crushed; optionally, the crushing equipment is one or more of a jaw crusher, mechanical mill, air jet mill, stirred mill, and ball mill; preferably, the particle size Dv50 of the crushed material is 3~30μm, more preferably 3~15μm.

[0020] The nitrogen used in this application has a purity of over 99.99%.

[0021] Secondly, this application provides a coal-based hard carbon anode material prepared by the method described above.

[0022] Thirdly, this application provides a negative electrode sheet, including the aforementioned coal-based hard carbon negative electrode material.

[0023] Fourthly, this application provides a sodium-ion secondary battery, including the aforementioned negative electrode sheet.

[0024] The technical solution of this invention has the following advantages: 1. The preparation method of the coal-based hard carbon anode material provided by the present invention includes the following steps: S1, activating coal powder to obtain activated coal powder; S2, mixing the activated coal powder with nano-scale thermoplastic resin to obtain a mixture, and pre-carbonizing the mixture; S3, carbonizing the product of S2 to obtain the coal-based hard carbon anode material; wherein the pre-carbonization step in S2 includes: placing the mixture in a mold, first filling the mold with nitrogen gas, heating to a first target temperature and holding at that temperature; then... Then, a first vacuum degassing and step-by-step molding are performed; after the step-by-step molding is completed, the temperature is raised to the second target temperature and held, and then nitrogen is injected for the second time; the first target temperature is above the melting point of the nano-scale thermoplastic resin; the step-by-step molding includes: first pressurizing to 0.2MPa~1MPa and holding for 10~15min; then each pressurization increases by 2~5MPa, and after each pressurization, it is held for 10~15min until the pressure rises to 15~18MPa; the second target temperature is 200~600℃.

[0025] This application first uses an activation method to enrich the pore structure of coal-based hard carbon, and then uses a special process to deeply integrate nanoscale thermoplastic resin with the formed pore structure in order to adjust its pore structure and ultimately solve the problem that coal has relatively poor performance as a sodium electrode anode.

[0026] Most of the volatiles have already been released after the coal powder is activated. At this point, the introduction of thermoplastic resin coating can make the thermoplastic resin and the activated coal powder come into closer contact. Thermoplastic resin has plasticity at high temperatures, and the melted nano-scale thermoplastic resin can uniformly coat the surface of the pre-carbonized coal-based hard carbon, making up for the structural defects of hard carbon. The introduction of molding greatly promotes the mutual integration of thermoplastic resin and activated coal powder.

[0027] In the pre-carbonization process of this application, the first vacuum exhaust is used to remove gas from the micropores of activated coal powder and molten resin. In the step-by-step molding process, the molding pressure is gradually increased to avoid the local enrichment or loss of thermoplastic resin caused by too rapid pressure increase due to a single pressurization. This ensures that the thermoplastic resin is evenly distributed in the activated coal powder, thereby significantly improving the specific capacity and initial efficiency of the material.

[0028] 2. The step of first filling the mold with nitrogen includes: nitrogen filling → second vacuum exhaust → nitrogen filling; wherein the nitrogen filling rate is 100~500ml / min; the second vacuum exhaust rate is 100~500ml / min; the second nitrogen filling rate is 100~500ml / min; and the first vacuum exhaust rate is 100~500ml / min. Controlling the nitrogen filling rate and vacuum exhaust rate can further prevent uneven material distribution in the mold. Detailed Implementation

[0029] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0030] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0031] Raw material source: Lump anthracite (Lanhua Kechuang: Lanhua brand), polyethylene (PE Yanshan Petrochemical: 3000JE (HDPE)), polypropylene (PP Brazil Braskem: C702-20), polystyrene (PS Arkema).

[0032] Example 1 This embodiment provides a method for preparing a coal-based hard carbon anode material, including the following steps: S1. Activate the pulverized coal to obtain activated pulverized coal: (1) Take 20g of lumpy anthracite and add it to a jaw crusher for coarse crushing until the coal particles reach the millimeter level. After coarse crushing, add the coarsely crushed coal to a ball mill for further crushing. The crushed particle size Dv50 is 5μm. Then, place the crushed coal powder in a polytetrafluoroethylene container and add a mixed acid solution prepared from deionized water, hydrochloric acid, and hydrofluoric acid. The concentrations of HCl and HF in the mixed acid solution are both 5mol / L, and the ratio of coal powder to mixed acid solution is 1g:3ml. Place the polytetrafluoroethylene container in an ultrasonic dispersion device for ultrasonic dispersion and acid washing deashing. The temperature of the ultrasonic disperser is 50℃ and the frequency is 200kHz. The ultrasonic and acid washing are performed for 12h. After acid washing, filter with deionized water and wash until the pH of the filtrate is 7. Dry in an oven at 120℃ for 12h to obtain acid-washed coal powder.

[0033] (2) Take 15g of acid-washed coal powder and activate it with steam at a temperature of 600℃ for 5 hours to obtain activated coal powder. The activation equipment is a tubular furnace.

[0034] S2. Mix activated coal powder with nano-scale thermoplastic resin to obtain a mixture, and then pre-carbonize the mixture: Activated coal powder and nano-sized polyethylene resin were mixed at a mass ratio of 10:1 to obtain a mixture; wherein the particle size of the nano-sized polyethylene resin was Dv50=50nm. The mixture was stirred evenly in a ball mill for 1 hour at a stirring speed of 300r / min.

[0035] The mixture was spread evenly in a mold, and nitrogen gas was introduced into the mold at a rate of 300 ml / min to 0.001 bar. Then, the mold was evacuated under vacuum at a rate of 300 ml / min to -1 bar, and then nitrogen gas was introduced again at a rate of 300 ml / min to 0.001 bar. The temperature was then increased to 130°C at a rate of 20°C / min and held for 4 hours. Vacuum gas was then evacuated under vacuum at a rate of 300 ml / min to -1 bar, followed by stepwise molding. The stepwise molding process included: first, pressurizing to 1 MPa and holding for 10 minutes; then increasing the pressure by 3 MPa each time, holding for 10 minutes after each pressurization, until the pressure reached 16 MPa. After stepwise molding, the temperature was increased to 400°C at a rate of 5°C / min and held for 4 hours, and then nitrogen gas was introduced into the mold at a rate of 300 ml / min to 0.001 bar.

[0036] S3. The product of S2 is subjected to carbonization treatment to obtain the coal-based hard carbon anode material: The product of S2 was added to an air jet mill to completely crush it. After secondary crushing, the particle size Dv50 of the material was 10 μm.

[0037] The product after secondary crushing is placed in a tubular furnace and carbonized at 1400℃ for 4 hours. The heating rate of the tubular furnace during carbonization is 10℃ / min, and the inert atmosphere during carbonization is nitrogen with a flow rate of 1L / min. After the tubular furnace cools to room temperature, the coal-based hard carbon anode material can be obtained.

[0038] Example 2 This embodiment provides a method for preparing a coal-based hard carbon anode material, including the following steps: S1. Activate the pulverized coal to obtain activated pulverized coal: (1) Take 20g of lumpy anthracite and add it to a jaw crusher for coarse crushing until the coal particles reach the millimeter level. After coarse crushing, add the coarsely crushed coal to a ball mill for further crushing. The crushed particle size Dv50 is 5μm. Then, place the crushed coal powder in a polytetrafluoroethylene container and add a mixed acid solution prepared from deionized water, hydrochloric acid, and hydrofluoric acid. The concentrations of HCl and HF in the mixed acid solution are both 5mol / L, and the ratio of coal powder to mixed acid solution is 1g:3ml. Place the polytetrafluoroethylene container in an ultrasonic dispersion device for ultrasonic dispersion and acid washing deashing. The temperature of the ultrasonic disperser is 50℃ and the frequency is 200kHz. The ultrasonic and acid washing are performed for 12h. After acid washing, filter with deionized water and wash until the pH of the filtrate is 7. Dry in an oven at 120℃ for 12h to obtain acid-washed coal powder.

[0039] (2) Take 15g of acid-washed coal powder and activate it with steam at a temperature of 600℃ for 5 hours to obtain activated coal powder. The activation equipment is a tubular furnace.

[0040] S2. Mix activated coal powder with nano-scale thermoplastic resin to obtain a mixture, and then pre-carbonize the mixture: Activated coal powder and nano-sized polypropylene (PP) resin were mixed at a mass ratio of 8:1 to obtain a mixture; wherein the particle size of the nano-sized polyethylene resin was Dv50=70nm. The mixture was stirred evenly in a ball mill for 1 hour at a stirring speed of 300r / min.

[0041] The mixture was spread evenly in a mold, and nitrogen gas was introduced into the mold at a rate of 200 ml / min to 0.001 bar. Then, the mold was evacuated under vacuum at a rate of 300 ml / min to -1 bar, and then nitrogen gas was introduced again at a rate of 200 ml / min to 0.001 bar. The temperature was then increased to 180°C at a rate of 15°C / min and held for 4 hours. Vacuum gas was then evacuated under vacuum at a rate of 200 ml / min to -1 bar, followed by stepwise molding. The stepwise molding process included: first, pressurizing to 0.5 MPa and holding for 15 minutes; then increasing the pressure by 2 MPa each time, holding for 15 minutes after each pressurization, until the pressure reached 16.5 MPa. After stepwise molding, the temperature was increased to 500°C at a rate of 5°C / min and held for 5 hours, and then nitrogen gas was introduced into the mold at a rate of 200 ml / min to 0.001 bar.

[0042] S3. The product of S2 is subjected to carbonization treatment to obtain the coal-based hard carbon anode material: The product of S2 was added to an air jet mill to completely crush it. After secondary crushing, the particle size Dv50 of the material was 10 μm.

[0043] The product after secondary crushing is placed in a tubular furnace and carbonized at 1400℃ for 4 hours. The heating rate of the tubular furnace during carbonization is 10℃ / min, and the inert atmosphere during carbonization is nitrogen with a flow rate of 1L / min. After the tubular furnace cools to room temperature, the coal-based hard carbon anode material can be obtained.

[0044] Example 3 This embodiment provides a method for preparing a coal-based hard carbon anode material, including the following steps: S1. Activate the pulverized coal to obtain activated pulverized coal: (1) Take 20g of lumpy anthracite and add it to a jaw crusher for coarse crushing until the coal particles reach the millimeter level. After coarse crushing, add the coarsely crushed coal to a ball mill for further crushing. The crushed particle size Dv50 is 5μm. Then, place the crushed coal powder in a polytetrafluoroethylene container and add a mixed acid solution prepared from deionized water, hydrochloric acid, and hydrofluoric acid. The concentrations of HCl and HF in the mixed acid solution are both 5mol / L, and the ratio of coal powder to mixed acid solution is 1g:3ml. Place the polytetrafluoroethylene container in an ultrasonic dispersion device for ultrasonic dispersion and acid washing deashing. The temperature of the ultrasonic disperser is 50℃ and the frequency is 200kHz. The ultrasonic and acid washing are performed for 12h. After acid washing, filter with deionized water and wash until the pH of the filtrate is 7. Dry in an oven at 120℃ for 12h to obtain acid-washed coal powder.

[0045] (2) Take 15g of acid-washed coal powder and activate it with steam at a temperature of 600℃ for 5 hours to obtain activated coal powder. The activation equipment is a tubular furnace.

[0046] S2. Mix activated coal powder with nano-scale thermoplastic resin to obtain a mixture, and then pre-carbonize the mixture: Activated coal powder and nano-sized polystyrene (PS) resin were mixed at a mass ratio of 9:1 to obtain a mixture; wherein the particle size of the nano-sized polyethylene resin was Dv50=70nm. The mixture was stirred uniformly using a ball mill for 1 hour at a stirring speed of 300r / min.

[0047] The mixture was spread evenly in a mold, and nitrogen gas was introduced into the mold at a rate of 400 ml / min to 0.001 bar. Then, the mold was evacuated under vacuum at a rate of 400 ml / min to -1 bar, and then nitrogen gas was introduced again at a rate of 400 ml / min to 0.001 bar. The temperature was then increased to 240°C at a rate of 20°C / min and held for 6 hours. The temperature was then evacuated under vacuum at a rate of 400 ml / min to -1 bar, followed by stepwise molding. The stepwise molding process included: first, pressurizing to 1 MPa and holding for 15 minutes; then increasing the pressure by 4 MPa each time, holding for 15 minutes after each pressurization, until the pressure reached 17 MPa. After stepwise molding, the temperature was increased to 600°C at a rate of 5°C / min and held for 4 hours, and then nitrogen gas was introduced into the mold at a rate of 400 ml / min to 0.001 bar.

[0048] S3. The product of S2 is subjected to carbonization treatment to obtain the coal-based hard carbon anode material: The product of S2 was added to an air jet mill to completely crush it. After secondary crushing, the particle size Dv50 of the material was 10 μm.

[0049] The product after secondary crushing is placed in a tubular furnace and carbonized at 1400℃ for 4 hours. The heating rate of the tubular furnace during carbonization is 10℃ / min, and the inert atmosphere during carbonization is nitrogen with a flow rate of 1L / min. After the tubular furnace cools to room temperature, the coal-based hard carbon anode material can be obtained.

[0050] Comparative Example 1 This comparative example provides a method for preparing a coal-based hard carbon anode material, including the following steps: S1. Activate the pulverized coal to obtain activated pulverized coal: (1) Take 20g of lumpy anthracite and add it to a jaw crusher for coarse crushing until the coal particles reach the millimeter level. After coarse crushing, add the coarsely crushed coal to a ball mill for further crushing. The crushed particle size Dv50 is 5μm. Then, place the crushed coal powder in a polytetrafluoroethylene container and add a mixed acid solution prepared from deionized water, hydrochloric acid, and hydrofluoric acid. The concentrations of HCl and HF in the mixed acid solution are both 5mol / L, and the ratio of coal powder to mixed acid solution is 1g:3ml. Place the polytetrafluoroethylene container in an ultrasonic dispersion device for ultrasonic dispersion and acid washing deashing. The temperature of the ultrasonic disperser is 50℃ and the frequency is 200kHz. The ultrasonic and acid washing are performed for 12h. After acid washing, filter with deionized water and wash until the pH of the filtrate is 7. Dry in an oven at 120℃ for 12h to obtain acid-washed coal powder.

[0051] (2) Take 15g of acid-washed coal powder and activate it with steam at a temperature of 600℃ for 5 hours to obtain activated coal powder. The activation equipment is a tubular furnace.

[0052] S2. The activated coal powder obtained in S1 is subjected to carbonization treatment to obtain the coal-based hard carbon anode material: Activated coal powder is placed in a tubular furnace and carbonized at 1400℃ for 4 hours. The heating rate of the tubular furnace during carbonization is 10℃ / min, and the inert atmosphere during carbonization is nitrogen with a flow rate of 1L / min. After the tubular furnace cools to room temperature, the coal-based hard carbon anode material can be obtained.

[0053] Comparative Example 2 This comparative example provides a method for preparing a coal-based hard carbon anode material, including the following steps: S1. Activate the pulverized coal to obtain activated pulverized coal: (1) Take 20g of lumpy anthracite and add it to a jaw crusher for coarse crushing until the coal particles reach the millimeter level. After coarse crushing, add the coarsely crushed coal to a ball mill for further crushing. The crushed particle size Dv50 is 5μm. Then, place the crushed coal powder in a polytetrafluoroethylene container and add a mixed acid solution prepared from deionized water, hydrochloric acid, and hydrofluoric acid. The concentrations of hydrochloric acid and hydrofluoric acid in the mixed acid solution are both 5mol / L, and the ratio of coal powder to mixed acid solution is 1g:3ml. Place the polytetrafluoroethylene container in an ultrasonic dispersion device for ultrasonic dispersion and acid washing deashing. The temperature of the ultrasonic disperser is 50℃ and the frequency is 200kHz. The ultrasonic and acid washing are performed for 12h. After acid washing, filter with deionized water and wash until the pH of the filtrate is 7. Dry in an oven at 120℃ for 12h to obtain acid-washed coal powder.

[0054] (2) Take 15g of acid-washed coal powder and activate it with steam at a temperature of 600℃ for 5 hours to obtain activated coal powder. The activation equipment is a tubular furnace.

[0055] S2. Mix activated coal powder with nano-scale thermoplastic resin to obtain a mixture, and then pre-carbonize the mixture: Activated coal powder and nano-sized polyethylene resin were mixed at a mass ratio of 10:1 to obtain a mixture; wherein the particle size of the nano-sized polyethylene resin was Dv50=50nm. The mixture was stirred evenly in a ball mill for 1 hour at a stirring speed of 300r / min.

[0056] The mixture was added to the reactor and heated to 130°C at a rate of 20°C / min under a nitrogen atmosphere, and held at that temperature for 4 hours. Then, the temperature was further increased to 400°C at a rate of 5°C / min and held for 4 hours.

[0057] S3. The product of S2 is subjected to carbonization treatment to obtain the coal-based hard carbon anode material: The product of S2 was added to an air jet mill to completely crush it. After secondary crushing, the particle size Dv50 of the material was 10 μm.

[0058] The product after secondary crushing is placed in a tubular furnace and carbonized at 1400℃ for 4 hours. The heating rate of the tubular furnace during carbonization is 10℃ / min, and the inert atmosphere during carbonization is nitrogen with a flow rate of 1L / min. After the tubular furnace cools to room temperature, the coal-based hard carbon anode material can be obtained.

[0059] Test case (1) Specific surface area of ​​coal-based hard carbon anode material, test standard GB / T 19587-2017.

[0060] (2) Uniformity of coal-based hard carbon anode material: Coal-based hard carbon anode material at different locations was sampled using the five-point sampling method, and its uniformity was tested by measuring the compaction density of coal-based hard carbon anode material at different sampling locations.

[0061] (3) The coal-based hard carbon anode material prepared in each embodiment and comparative example is used as the anode, metallic sodium is used as the cathode, the solute of the electrolyte is sodium hexafluorophosphate, the solvent is a mixture of ethylene carbonate and dimethyl carbonate = 1:1, and the electrolyte concentration is 1M; and they are assembled into button cells.

[0062] The specific capacity and initial coulombic efficiency of the battery are tested using the following steps: 1. Settling: After the battery is assembled, let it stand at 25°C for 8 hours to ensure that the electrolyte fully wets the electrode materials and separator, and to eliminate the interfacial stress that may be generated during the assembly process.

[0063] 2. Constant current charge-discharge test: Step 1: Constant current discharge, current density: 0.1C, cutoff voltage: 0.01V; Step 2: Let it rest for 20 minutes; Step 3: Constant current charging, 0.1C, charging to 2V; Step 4: Let it rest for 20 minutes; Step 5: Repeat steps 1 to 4 twice; Step 6: End.

[0064] The test results are shown in Tables 1 and 2.

[0065] Table 1

[0066] As shown in Table 1, the compaction density range of the coal-based hard carbon anode material at different locations prepared by the method of this application is ≤0.002, which is significantly lower than the range of Comparative Example 2. This means that the compaction density of the coal-based hard carbon anode material of this application remains highly consistent, proving that it has good uniformity and there is no problem of local enrichment or absence of thermoplastic resin.

[0067] Table 2

[0068] As shown in Table 2, the specific capacity and initial coulombic efficiency of the coal-based hard carbon anode material prepared in this application are significantly improved.

[0069] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a coal-based hard carbon anode material, characterized in that, Includes the following steps: S1. Activate the coal powder to obtain activated coal powder; S2. The activated coal powder is mixed with nano-scale thermoplastic resin to obtain a mixture, and the mixture is subjected to pre-carbonization treatment; S3. The product of S2 is subjected to carbonization treatment to obtain the coal-based hard carbon anode material. In step S2, the pre-carbonization process includes: placing the mixture into a mold, filling the mold with nitrogen for the first time, heating to a first target temperature and holding it at that temperature; then performing a first vacuum degassing and step-by-step molding; after the step-by-step molding is completed, heating to a second target temperature and holding it at that temperature, and then filling with nitrogen for the second time. The first target temperature is above the melting point of the nanoscale thermoplastic resin; The stepwise molding process includes: first pressurizing to 0.2MPa~1MPa and holding for 10~15min; then increasing the pressure by 2~5MPa each time, and holding for 10~15min after each pressurization, until the pressure rises to 15~18MPa; The second target temperature is 200~600℃.

2. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, S2 satisfies at least one of the following conditions: (1) The step of first filling the mold with nitrogen includes: filling with nitrogen → second vacuum exhaust → filling with nitrogen; The nitrogen filling rate is 100~500ml / min; The exhaust speed of the second vacuum exhaust is 100~500ml / min; (2) The second nitrogen filling rate is 100~500ml / min; (3) The exhaust speed of the first vacuum exhaust is 100~500ml / min.

3. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that, S2 satisfies at least one of the following conditions: (1) The first target temperature is 10~20°C above the melting point of the nano-scale thermoplastic resin; (2) The holding time for heating to the first target temperature and maintaining the temperature is 2~8h; (3) The heating rate to the first target temperature is 15~20℃ / min; (4) The holding time for raising the temperature to the second target temperature and holding it is 1~10h; (5) The heating rate to the second target temperature is 3~6℃ / min; (6) The second target temperature is 300~500℃.

4. The method for preparing the coal-based hard carbon anode material according to claim 1, characterized in that... S2 satisfies at least one of the following conditions: (1) The mass ratio of the activated coal powder to the nano-scale thermoplastic resin is (6~10):1; (2) The particle size Dv50 of the nano-scale thermoplastic resin is 10~300nm, preferably 20~100nm; (3) The nano-scale thermoplastic resin includes one or more of polycaprolactone, polyethylene, polypropylene, polystyrene, polyamide, and polyethylene terephthalate.

5. The method for preparing the coal-based hard carbon anode material according to any one of claims 1-4, characterized in that, S1 satisfies at least one of the following conditions: (1) The particle size Dv50 of the pulverized coal is 3~30μm, preferably 3~15μm; (2) The pulverized coal is obtained by crushing coal, and the coal is selected from one or more of bituminous coal, sub-bituminous coal, and anthracite; Optionally, the pulverized coal is obtained through coal crushing, acid washing, water washing, and drying; Optionally, the acid used for pickling is one or more of hydrochloric acid, hydrofluoric acid, and nitric acid; Optionally, the pickling temperature is 40~70℃, and the time is 0.5~24h; Optionally, the drying temperature is 105-120℃ and the drying time is 5-24h.

6. The method for preparing the coal-based hard carbon anode material according to any one of claims 1-4, characterized in that, In step S1, steam is used to activate the pulverized coal. Optionally, the activation temperature is 450~900℃, preferably 600~800℃; Optionally, the activation time is 2-6 hours, preferably 3-5 hours; Optionally, the equipment used for activation may be one or more of the following: tube furnace, box furnace, and rotary furnace.

7. The method for preparing the coal-based hard carbon anode material according to any one of claims 1-4, characterized in that, S3 satisfies at least one of the following conditions: (1) The carbonization temperature is 800~1600℃, preferably 1000~1400℃; (2) The carbonization treatment time is 0.5~6h, preferably 2~4h; (3) The heating rate to the carbonization treatment temperature is 1~20℃ / min, preferably 1~10℃ / min.

8. A coal-based hard carbon anode material prepared by the method according to any one of claims 1-7.

9. A negative electrode sheet, characterized in that, Including the coal-based hard carbon anode material as described in claim 8.

10. A sodium-ion secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

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