A method for preparing a sodium-ion battery hard carbon negative electrode material by using papermaking black slurry and application

Abstract

The application provides a method for preparing a hard carbon negative electrode material for a sodium ion battery by using papermaking black slurry and application, and belongs to the technical field of sodium ion battery materials. The method uses papermaking black slurry as a precursor, and sequentially performs mixed acid cooking and purification, washing and drying, vacuum annealing, particle size control and high-temperature carbonization processes to prepare the hard carbon negative electrode material for the sodium ion battery. Through the whole-process synergistic process of mixed acid synergistic cooking, structure-preserving drying, vacuum annealing and controllable rate carbonization, the application realizes deep impurity removal of the papermaking black slurry and accurate regulation of the microstructure of the hard carbon, and prepares a high-performance hard carbon negative electrode material with high initial efficiency, high capacity and low specific surface area. Meanwhile, the application realizes resource utilization of industrial waste and reduces the preparation cost of the sodium ion battery material.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery materials technology, and in particular to a method and application for preparing hard carbon anode materials for sodium-ion batteries using papermaking black pulp. Background Technology

[0002] Hard carbon materials have become a preferred anode material for sodium-ion batteries due to their low cost, suitable sodium ion insertion / extraction potential, and abundant resources. Finding widely available and inexpensive precursors is key to reducing the cost of hard carbon materials. Biomass raw materials, especially industrial byproducts, have become a research hotspot for hard carbon precursors because of their combination of resource availability and economic viability.

[0003] Papermaking black pulp (including wood black pulp and non-wood black pulp) is a dark-colored byproduct produced during the papermaking pulping process, with lignin as the main component. It has a large output and wide range of sources. Moreover, lignin is an aromatic polymer with an amorphous three-dimensional network structure, which is a natural and high-quality carbon source for the preparation of hard carbon.

[0004] Although papermaking black pulp has the component basis of hard carbon precursors, its high-value utilization faces significant technical bottlenecks: First, its complex composition and high impurity content lead to ash residues in the carbon skeleton during carbonization, damaging the material's conductivity and becoming active sites for electrochemical side reactions, resulting in low battery capacity, poor coulombic efficiency, and reduced cycle life. Second, its disordered structure makes it difficult for untreated black pulp to form an ideal hard carbon microstructure under conventional carbonization, resulting in poor pore structure and uncontrolled specific surface area, which cannot meet the performance requirements of sodium-ion batteries. Third, existing pretreatment technologies have defects, mostly using single acid washing or water washing, which has limited purification effects and is difficult to deeply remove stable silicate impurities. Furthermore, conventional atmospheric pressure high-temperature drying easily leads to shrinkage of the precursor gel network and collapse of pores after acid washing, and inert atmosphere atmospheric pressure annealing cannot completely remove small molecule impurities, easily generating harmful pores, ultimately resulting in low initial efficiency and unstable performance of hard carbon materials.

[0005] Current technologies cannot simultaneously address the dual challenges of deep purification of papermaking black pulp and preservation of precursor microstructure, preventing it from becoming a reliable high-performance hard carbon precursor. Therefore, developing a preparation method that achieves deep purification of papermaking black pulp and effectively maintains and optimizes its sodium-friendly microstructure in subsequent processes is not only an urgent need for the high-value utilization of industrial waste but also a highly promising approach to solving the cost problem of sodium-ion battery anode materials. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for preparing hard carbon anode materials for sodium-ion batteries using papermaking black pulp, which solves the problems of the difficulty in high-value utilization of papermaking black pulp and the inability of pretreatment to simultaneously achieve deep purification and microstructure preservation in the prior art. At the same time, this invention will also provide a method for preparing hard carbon anode materials for sodium-ion batteries using the above-described preparation method; in addition, this invention will also provide the application of the above-described hard carbon anode materials for sodium-ion batteries in sodium-ion batteries.

[0007] To achieve the above and other related objectives, the present invention provides the following technical solutions: A first aspect of the present invention provides a method for preparing hard carbon anode material for sodium-ion batteries using papermaking black pulp, comprising the following steps: (1) The papermaking black pulp is mixed with the mixed acid solution and cooked under heating conditions with continuous stirring; (2) Wash the material after cooking in step (1) with distilled water until neutral, and then perform structure-preserving drying to obtain purified black pulp powder; (3) Place the purified black paste powder obtained in step (2) in a carbonization furnace, evacuate the system to a relative pressure of -50Pa ~ -2Pa, and anneal it at a temperature of 600℃~1100℃ to obtain an annealing intermediate. (4) The annealing intermediate obtained in step (3) is crushed and sieved to obtain a powder with uniform particle size, so as to ensure the consistency of subsequent electrochemical performance. (5) The powder obtained in step (4) is subjected to high-temperature carbonization under a protective atmosphere to obtain a hard carbon anode material for sodium-ion batteries.

[0008] Further, in step (1), the mixed acid solution is composed of hydrochloric acid, sulfuric acid, and nitric acid. Specifically, the mixed acid solution is composed of concentrated hydrochloric acid, concentrated sulfuric acid, and concentrated nitric acid, with a volume ratio of (10~50):(5~40):(15~40); preferably, the volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid, and concentrated nitric acid is (20~40):(10~30):(20~35).

[0009] Furthermore, in step (1), the papermaking black pulp is wood black pulp or non-wood black pulp; the ratio of the papermaking black pulp to the mixed acid is 1g:(1~5)mL.

[0010] Furthermore, in step (1), the heating and cooking temperature is 60℃~100℃, and the time is 2~8 hours.

[0011] Step (1) achieves deep removal of impurities and modification of carbon skeleton functional groups through mixed acid cooking, improves the purity of hard carbon, and forms a preliminary porous structure.

[0012] Furthermore, in step (2), the cooked material is repeatedly washed with distilled water and filtered until the filtrate is neutral to remove residual acid and dissolved impurities.

[0013] Furthermore, in step (2), the structure-preserving drying is selected from one or more combinations of vacuum low-temperature drying, low-temperature low-pressure rotary evaporation, and freeze drying. These drying methods effectively prevent the shrinkage of the precursor gel network and the collapse of the pores by reducing the surface tension of the liquid phase during the drying process or by directly sublimating water, thus preserving the open and abundant mesoscopic structure formed after acid treatment. This lays the foundation for the formation of ideal, sodium-ion-friendly closed micropores rather than harmful large specific surface area open pores during the subsequent carbonization process.

[0014] Among them, vacuum low-temperature drying is drying at 60℃ and -0.09 MPa for 12 hours; Low-temperature and low-pressure rotary evaporation involves using a rotary evaporator for drying, with the water bath temperature set at 50°C and the system vacuum maintained at -0.06 MPa. Freeze-drying involves drying the filter cake using a freeze-drying method, with pre-freezing at -40℃ and main drying at -20℃.

[0015] Furthermore, in step (3), the heating rate of the annealing treatment is 1~10℃ / min, and after reaching the set temperature, the holding time is 0.5~4 hours.

[0016] The vacuum annealing in step (3) is carried out in an oxygen-free and strongly vented environment to completely remove small molecule impurities, while purifying and solidifying the carbon skeleton to form a dense, low-defect graphite microcrystalline region, which is beneficial to improving the conductivity and tap density of the material.

[0017] Furthermore, in step (4), the powder is pulverized by ball milling, grinding, etc., and then sieved through a standard sieve; the D50 of the obtained powder is 5~10μm.

[0018] Furthermore, in step (5), the protective atmosphere is nitrogen or argon.

[0019] Furthermore, in step (5), the temperature of the high-temperature carbonization treatment is 1000℃~1400℃, the heating rate is 2~10℃ / min, and the holding time is 1~5 hours.

[0020] In a second aspect, the present invention provides a hard carbon anode material for sodium-ion batteries, which is prepared by the above-described preparation method.

[0021] A third aspect of the present invention provides an application of the above-mentioned hard carbon anode material for sodium-ion batteries in sodium-ion batteries, wherein the resulting sodium-ion battery has an initial coulombic efficiency of not less than 89%, a reversible specific capacity of not less than 350 mAh / g, and a BET specific surface area of ​​4.0~9.0 m². 2 / g.

[0022] As described above, the method and application of the present invention for preparing hard carbon anode materials for sodium-ion batteries using papermaking black pulp have the following beneficial effects: 1. Precise Structure Control Achieved Through Full-Process Collaboration: Mixed acid cooking achieves deep impurity removal and preliminary pore structure / functional group modification; the synergistic effect of three acids overcomes the purification bottleneck of single acid washing; structure-preserving drying effectively prevents precursor gel network shrinkage and pore collapse by reducing liquid phase surface tension or directly sublimating water, preserving the sodium-storage-friendly open mesoscopic structure; vacuum annealing achieves secondary purification and carbon skeleton solidification in an oxygen-free and strongly exhaust-free environment, inhibiting the formation of harmful pores and improving the material's conductivity and tap density; controllable-rate high-temperature carbonization promotes the formation of expanded graphite microcrystalline structures, providing abundant active sites for sodium ion storage; each process step is interconnected and works synergistically, solving the core problem of the difficulty in simultaneously achieving purification and structure preservation.

[0023] 2. Excellent and balanced product performance: Through the process of this invention, a product with an initial coulombic efficiency of over 89%, a reversible specific capacity of over 350 mAh / g, and a BET specific surface area controlled between 4 and 9 m² is successfully prepared. 2 The low-range hard carbon material with a specific surface area of ​​ / g effectively reduces irreversible side reactions during the first charge and discharge cycle, which is the key to achieving high initial efficiency and long cycle life. The comprehensive performance of the material meets the requirements of the industrial application of sodium-ion batteries.

[0024] 3. Low-cost raw materials and high-value utilization of waste: Using papermaking black pulp, a byproduct of the papermaking industry, as raw material, it has a wide range of sources and extremely low prices, replacing traditional hard carbon precursors such as resin and glucose, and significantly reducing raw material costs; at the same time, it solves the environmental pollution problem of traditional papermaking black pulp disposal methods, realizes the resource utilization of industrial solid waste, and has significant environmental and economic value.

[0025] 4. The process is simple and controllable, suitable for industrial scale-up: The steps of cooking, drying, annealing, carbonization, and sieving in this invention are all common industrial chemical operations, without special or complex equipment requirements; the process window is wide, and when parameters such as the mixed acid ratio, annealing temperature, carbonization temperature, and drying method are adjusted within a certain range, the product performance can still stably reach the predetermined indicators, avoiding the parameter adaptation problem of industrial scale-up of laboratory processes, and the entire process has no high-pollution or high-energy-consumption extra links, making the production process green and environmentally friendly. Attached Figure Description

[0026] Figure 1This is the X-ray diffraction (XRD) pattern of the hard carbon anode material prepared in Example 1 of the present invention.

[0027] Figure 2 This is a scanning electron microscope (SEM) image of the hard carbon anode material prepared in Example 1 of the present invention.

[0028] Figure 3 The first charge-discharge curve of a sodium-ion half-cell assembled using the hard carbon anode material prepared in Example 1 of this invention. Detailed Implementation

[0029] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0030] Based on the method described in this invention, the technical effects of this invention are further illustrated below through specific embodiments and comparative examples. In the following embodiments and comparative examples, the equipment, instruments, and solutions used are commonly used in the art, wherein the concentration of concentrated hydrochloric acid is 37%, the concentration of concentrated sulfuric acid is 98%, and the concentration of concentrated nitric acid is 65%; the papermaking black pulp in the embodiments and comparative examples is the same.

[0031] Example 1 This embodiment provides a method for preparing hard carbon anode materials for sodium-ion batteries using papermaking black pulp, including the following steps: (1) Purification by cooking with mixed acid: Take 100g of papermaking black pulp and mix it with 200mL of mixed acid solution (the volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid and concentrated nitric acid is 30:30:35). Place the mixture in a reactor and cook it continuously at 100℃ for 4 hours.

[0032] (2) Structure-preserving drying: The material after cooking in step (1) is washed with distilled water and filtered until neutral. Then the filter cake is placed in a vacuum drying oven and dried for 12 hours at 60°C and -0.09 MPa to obtain purified black pulp powder.

[0033] (3) Vacuum annealing: The purified black paste powder obtained in step (2) is placed in a vacuum carbonization furnace, and the system relative pressure is evacuated to -50Pa. The temperature is increased to 600℃ at 5℃ / min, and the temperature is maintained for 2 hours before cooling with the furnace to obtain the annealed intermediate.

[0034] (4) Particle size control: The annealing intermediate obtained in step (3) is ground and sieved to obtain a uniform powder with a D50 of 5.7 μm.

[0035] (5) High-temperature carbonization: The powder obtained in step (4) is heated to 1300℃ at 2℃ / min under argon protection, and then naturally cooled after holding for 3 hours to obtain hard carbon anode material, denoted as HC-1.

[0036] Example 2 This embodiment provides a method for preparing hard carbon anode materials for sodium-ion batteries using papermaking black pulp, including the following steps: (1) Purification by cooking with mixed acid: Take 100g of papermaking black pulp and mix it with 200mL of mixed acid solution (the volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid and concentrated nitric acid is 40:25:35). Place the mixture in a reactor and cook it continuously at 100℃ for 4 hours.

[0037] (2) Structure-preserving drying: The material after cooking in step (1) is washed with distilled water and filtered until neutral. Then the filter cake is placed in a vacuum drying oven and dried for 12 hours at 60°C and -0.09 MPa to obtain purified black pulp powder.

[0038] (3) Vacuum annealing: The purified black paste powder obtained in step (2) is placed in a vacuum carbonization furnace, and the system relative pressure is evacuated to -2Pa. The temperature is increased to 800℃ at 5℃ / min, and the temperature is maintained for 2 hours before cooling with the furnace to obtain the annealing intermediate.

[0039] (4) Particle size control: The annealing intermediate obtained in step (3) is ground and sieved to obtain a uniform powder with a D50 of 5.2 μm.

[0040] (5) High-temperature carbonization: The powder obtained in step (4) is heated to 1300°C at 5°C / min under argon protection, and then naturally cooled after holding for 3 hours to obtain hard carbon anode material, denoted as HC-2.

[0041] Example 3 This embodiment provides a method for preparing hard carbon anode materials for sodium-ion batteries using papermaking black pulp, including the following steps: (1) Purification by cooking with mixed acid: Take 100g of papermaking black pulp and mix it with 200mL of mixed acid solution (the volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid and concentrated nitric acid is 40:35:25). Place the mixture in a reactor and cook it continuously at 100℃ for 4 hours.

[0042] (2) Structure-preserving drying: The material after cooking in step (1) is washed with distilled water and filtered until neutral. Then the filter cake is placed in a vacuum drying oven and dried for 12 hours at 60°C and -0.09 MPa to obtain purified black pulp powder.

[0043] (3) Vacuum annealing: The purified black paste powder obtained in step (2) is placed in a vacuum carbonization furnace, and the system relative pressure is evacuated to -2Pa. The temperature is increased to 800℃ at 5℃ / min, and the temperature is maintained for 2 hours before cooling with the furnace to obtain the annealing intermediate.

[0044] (4) Particle size control: The annealing intermediate obtained in step (3) is ground and sieved to obtain a uniform powder with a D50 of 7.9 μm.

[0045] (5) High-temperature carbonization: The powder obtained in step (4) is heated to 1100°C at 3°C / min under argon protection, and then naturally cooled after holding at the temperature for 3 hours to obtain a hard carbon anode material, denoted as HC-3.

[0046] Example 4 This embodiment provides a method for preparing hard carbon anode materials for sodium-ion batteries using papermaking black pulp, including the following steps: (1) Purification by cooking with mixed acid: Take 100g of papermaking black pulp and mix it with 200mL of mixed acid solution (the volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid and concentrated nitric acid is 40:15:35). Place the mixture in a reactor and cook it continuously at 100℃ for 4 hours.

[0047] (2) Structure-preserving drying: The material after cooking in step (1) is washed with distilled water and filtered until neutral. Then, the filter cake is freeze-dried at a pre-freezing temperature of -40℃ and a main drying temperature of -20℃ to obtain purified black pulp powder.

[0048] (3) Vacuum annealing: The purified black paste powder obtained in step (2) is placed in a vacuum carbonization furnace, and the system relative pressure is evacuated to -50Pa. The temperature is increased to 800℃ at 5℃ / min, and the temperature is maintained for 2 hours before cooling with the furnace to obtain the annealing intermediate.

[0049] (4) Particle size control: The annealing intermediate obtained in step (3) is ground and sieved to obtain a uniform powder with a D50 of 6.0 μm.

[0050] (5) High-temperature carbonization: The powder obtained in step (4) is heated to 1000°C at 7°C / min under argon protection, and then naturally cooled after holding at the temperature for 3 hours to obtain a hard carbon anode material, denoted as HC-4.

[0051] Example 5 This embodiment provides a method for preparing hard carbon anode materials for sodium-ion batteries using papermaking black pulp, including the following steps: (1) Purification by cooking with mixed acid: Take 100g of papermaking black pulp and mix it with 200mL of mixed acid solution (the volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid and concentrated nitric acid is 40:25:35). Place the mixture in a reactor and cook it continuously at 100℃ for 4 hours.

[0052] (2) Structure-preserving drying: The material after cooking in step (1) is washed with distilled water and filtered until neutral. Then the filter cake is placed in a vacuum drying oven and dried for 12 hours at 60°C and -0.09 MPa to obtain purified black pulp powder.

[0053] (3) Vacuum annealing: The purified black paste powder obtained in step (2) is placed in a vacuum carbonization furnace, and the system relative pressure is evacuated to -50Pa. The temperature is increased to 800℃ at 10℃ / min, and the temperature is maintained for 2 hours before cooling with the furnace to obtain the annealing intermediate.

[0054] (4) Particle size control: The annealing intermediate obtained in step (3) is ground and sieved to obtain a uniform powder with a D50 of 5.2 μm.

[0055] (5) High-temperature carbonization: The powder obtained in step (4) is heated to 1300°C at 10°C / min under argon protection, and then naturally cooled after holding for 3 hours to obtain hard carbon anode material, denoted as HC-5.

[0056] Example 6 This embodiment provides a method for preparing hard carbon anode materials for sodium-ion batteries using papermaking black pulp, including the following steps: (1) Purification by cooking with mixed acid: Take 100g of papermaking black pulp and mix it with 200mL of mixed acid solution (the volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid and concentrated nitric acid is 30:30:35). Place the mixture in a reactor and cook it continuously at 100℃ for 4 hours.

[0057] (2) Structure-preserving drying: The material after cooking in step (1) is washed with distilled water and filtered until neutral. Then the filter cake is placed in a vacuum drying oven and dried for 12 hours at 60°C and -0.09 MPa to obtain purified black pulp powder.

[0058] (3) Vacuum annealing: The purified black paste powder obtained in step (2) is placed in a vacuum carbonization furnace, and the system relative pressure is evacuated to -2Pa. The temperature is increased to 800℃ at 5℃ / min, and the temperature is maintained for 2 hours before cooling with the furnace to obtain the annealing intermediate.

[0059] (4) Particle size control: The annealing intermediate obtained in step (3) is ground and sieved to obtain a uniform powder with a D50 of 6.8 μm.

[0060] (5) High-temperature carbonization: The powder obtained in step (4) is heated to 1400°C at 3°C / min under argon protection, and then naturally cooled after holding at the temperature for 3 hours to obtain a hard carbon anode material, denoted as HC-6.

[0061] Comparative Example 1 This comparative example provides a method for preparing a hard carbon anode material. The only difference from Example 1 is that the vacuum annealing in step (3) is replaced by annealing under normal pressure argon atmosphere with an argon flow rate of 200 sccm. The remaining steps and parameters are the same as in Example 1. The resulting hard carbon anode material is denoted as DBC-1.

[0062] Comparative Example 2 This comparative example provides a method for preparing a hard carbon anode material. The only difference from Example 1 is that the heating rate of high-temperature carbonization in step (5) is increased to 20℃ / min. The remaining steps and parameters are the same as in Example 1. The hard carbon anode material obtained is denoted as DBC-2.

[0063] Comparative Example 3 This comparative example provides a method for preparing a hard carbon anode material. The only difference from Example 1 is that the structure-preserving drying in step (2) is replaced by 105°C atmospheric pressure forced air drying. The remaining steps and parameters are the same as in Example 1. The resulting hard carbon anode material is denoted as DBC-3.

[0064] Comparative Example 4 This comparative example provides a method for preparing a hard carbon anode material. The only difference from Example 1 is that in the mixed acid in step (1), the ratio of concentrated hydrochloric acid: concentrated sulfuric acid: concentrated nitric acid = 50:40:10, and the proportion of nitric acid is lower than that of this invention. The remaining steps and parameters are the same as in Example 1, and the material DBC-4 is obtained.

[0065] Comparative Example 5 This comparative example provides a method for preparing a hard carbon anode material. The only difference from Example 1 is that the vacuum annealing temperature in step (3) is increased to 1200°C, which is beyond the protection scope of this invention. The remaining steps and parameters are the same as in Example 1. The hard carbon anode material obtained is denoted as DBC-5.

[0066] Performance testing The hard carbon anode materials prepared in Examples 1-6 and Comparative Examples 1-5 were used to prepare sodium-ion half-cells, and their electrochemical and physical properties were tested using the following methods: 1. Electrode preparation: Prepare a polyvinylidene fluoride solution with a mass fraction of 6-7% using N-methylpyrrolidone as solvent. Mix the hard carbon negative electrode material, polyvinylidene fluoride, and conductive carbon black with the polyvinylidene fluoride solution at a mass ratio of 90:5:5. Coat the mixture onto copper foil. Place the coated electrode in a vacuum drying oven at 110℃ and vacuum dry for 4 hours. Cut the electrode into small round pieces with a diameter of 14mm.

[0067] 2. Battery assembly: The 2430 button cell was assembled in an argon-filled German Micron glove box. The electrolyte was a three-component mixed solvent of 1 mol / L NaPF6 in a volume ratio of EC:DMC:EMC=1:1:1. The counter electrode was a sodium metal sheet, and the separator was a 16 μm thick Ube membrane.

[0068] 3. Performance testing: The assembled half-cells were tested for electrochemical performance using the Arbin electrochemical testing system in the United States. The charge and discharge voltage range was 0V to 2.0V, the rate was 0.1C, and the cycle test rate was 1C.

[0069] The specific surface area of ​​the hard carbon anode material was measured using a BET surface area analyzer, and the particle size D50 was measured using a laser particle size analyzer.

[0070] Test Results and Analysis The materials prepared in the above embodiments and comparative examples were assembled into sodium-ion half-cells for testing. The performance data are summarized in the table below:

[0071] The test results show that: 1. The hard carbon anode materials prepared in Examples 1-6 all stably achieved a reversible specific capacity ≥350mAh / g, an initial coulombic efficiency ≥89%, and a specific surface area of ​​4.0~9.0m². 2 The technical indicator / g proves that the technical solution of the present invention has a reliable process window, and the product performance is stable when the parameters are adjusted within the protection range, making it suitable for industrial production.

[0072] 2. Comparative Example 1 uses atmospheric pressure argon annealing instead of vacuum annealing, resulting in a significant increase in the specific surface area of ​​the material and a substantial decrease in capacity and first-time efficiency. This demonstrates that a vacuum environment is a necessary condition for suppressing the formation of harmful pores and achieving high first-time efficiency.

[0073] The carbonization heating rate of Comparative Example 2 was too fast, resulting in insufficient formation of the hard carbon structure and a significant reduction in performance, proving that a controllable slow heating rate is beneficial for the formation of a stable sodium storage structure.

[0074] Comparative Example 3 used atmospheric pressure high temperature drying, which caused the precursor pores to collapse, reduced sodium storage active sites, and decreased capacity and first-efficiency. This proves that structure-preserving drying plays a key role in maintaining the beneficial structure of the precursor and controlling the final specific surface area, and is a key step in this invention.

[0075] Comparative Example 4 showed that the proportion of nitric acid was too low, which could not effectively modify the functional groups and the first-effect was not met, proving that the synergistic ratio of the three acids is indispensable.

[0076] The annealing temperature of Comparative Example 5 was too high, resulting in excessive etching of the carbon skeleton, an increase in harmful porosity, and a decrease in performance, proving that the annealing temperature needs to be within the optimized range of this invention.

[0077] The above test results fully demonstrate that each core link in the entire process chain of the present invention, namely "mixed acid synergistic cooking - structure-preserving drying - vacuum annealing - controllable rate carbonization", is original and irreplaceable. The absence of any key step or deviation of parameters will result in the product performance failing to meet the high-performance standards of the present invention.

[0078] In summary, this invention uses papermaking black pulp, a byproduct of the papermaking industry, as a precursor. Through a comprehensive synergistic process involving mixed acid synergistic cooking, structure-preserving drying, vacuum annealing, and controllable-rate carbonization, it achieves deep deimpurification of the papermaking black pulp and precise control of the hard carbon microstructure. This results in the preparation of high-efficiency, high-capacity, and low-specific-surface-area high-performance hard carbon anode materials, while simultaneously realizing the resource utilization of industrial waste and reducing the manufacturing cost of sodium-ion battery materials. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial application value.

[0079] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing hard carbon anode material for sodium-ion batteries using papermaking black pulp, characterized in that, Includes the following steps: (1) The papermaking black pulp is mixed with the mixed acid solution and cooked under heating conditions with continuous stirring; (2) Wash the material after cooking in step (1) with distilled water until neutral, and then perform structure-preserving drying to obtain purified black pulp powder; (3) Place the purified black paste powder obtained in step (2) in a carbonization furnace, evacuate the system to a relative pressure of -50Pa to -2Pa, and anneal it at a temperature of 600℃ to 1100℃ to obtain an annealing intermediate. (4) The annealing intermediate obtained in step (3) is crushed and sieved to obtain a powder with uniform particle size; (5) The powder obtained in step (4) is subjected to high-temperature carbonization under a protective atmosphere to obtain a hard carbon anode material for sodium-ion batteries.

2. The method according to claim 1, characterized in that, In step (1), the mixed acid solution is composed of hydrochloric acid, sulfuric acid and nitric acid.

3. The method according to claim 2, characterized in that, In step (1), the mixed acid solution is composed of concentrated hydrochloric acid, concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of concentrated hydrochloric acid, concentrated sulfuric acid and concentrated nitric acid is (20~40):(10~30):(20~35).

4. The method according to claim 1, characterized in that, In step (1), the papermaking black pulp is wood black pulp or non-wood black pulp; the ratio of the papermaking black pulp to the mixed acid is 1g:(1~5)mL.

5. The method according to claim 1, characterized in that, In step (1), the heating and cooking temperature is 60℃~100℃ and the time is 2~8 hours.

6. The method according to claim 1, characterized in that, In step (2), the structure-preserving drying is selected from one or more combinations of vacuum low-temperature drying, low-temperature low-pressure rotary evaporation, and freeze drying.

7. The method according to claim 6, characterized in that, The vacuum low-temperature drying is performed at 60°C and -0.09 MPa for 12 hours. The low-temperature, low-pressure rotary evaporation is performed using a rotary evaporator, with the water bath temperature set at 50°C and the system vacuum maintained at -0.06 MPa. The freeze-drying process involves drying the filter cake using a freeze-drying method, with pre-freezing at -40°C and main drying at -20°C.

8. The method according to claim 1, characterized in that, In step (3), the heating rate of the annealing treatment is 1~10℃ / min, and after reaching the set temperature, the holding time is 0.5~4 hours.

9. The method according to claim 1, characterized in that, In step (5), the temperature of the high-temperature carbonization treatment is 1000℃~1400℃, the heating rate is 2~10℃ / min, and the holding time is 1~5 hours.

10. The application of a sodium-ion battery hard carbon anode material prepared by the method according to any one of claims 1 to 9 in a sodium-ion battery, characterized in that, The obtained sodium-ion battery exhibits an initial coulombic efficiency of no less than 89%, a reversible specific capacity of no less than 350 mAh / g, and a BET specific surface area of ​​4.0~9.0 m². 2 / g.

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