Preparation method and application of waste viscose fiber hard carbon material

Abstract

This invention provides a method and application for preparing hard carbon materials from waste viscose fibers. The preparation method includes washing and drying the waste viscose fibers to obtain a first precursor; subjecting the first precursor to low-temperature heat treatment to obtain a second precursor; and carbonizing the second precursor at high temperature to obtain the hard carbon material. This invention preserves the morphology of the fibers, and after carbonization, a three-dimensional interconnected conductive network is naturally formed, improving the reversible specific capacity, rate capability, and cycle stability of the battery. By combining simple treatment of waste viscose fibers with a stepwise carbonization process, a sodium-ion battery hard carbon anode material with large carbon interlayer spacing and excellent electrochemical performance is obtained. The materials used in this invention are inexpensive, readily available, and suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery anode materials, specifically relating to a method for preparing and applying a waste viscose fiber hard carbon material. Background Technology

[0002] With the large-scale grid connection of renewable energy and the rapid development of smart grids, there is an urgent need for large-scale, low-cost, and highly safe electrochemical energy storage systems. Sodium-ion batteries, due to the abundance and wide distribution of sodium resources, their low cost, and their similar working principle to lithium-ion batteries, are considered a key candidate for next-generation large-scale energy storage technology. The anode material is one of the key components determining the performance, cost, and industrialization prospects of sodium-ion batteries. Because of the large radius of sodium ions, traditional graphite anodes exhibit poor thermodynamic and kinetic performance in storing sodium ions in carbonate electrolytes, resulting in extremely low capacity. Therefore, developing novel anode materials suitable for sodium-ion batteries has become a research focus.

[0003] Among numerous candidate materials, hard carbon materials are considered one of the most promising anode materials for sodium-ion batteries due to their abundant defects, large interlayer spacing, low cost, and high reversible capacity. Currently, the raw materials for preparing hard carbon materials mainly include biomass precursors and synthetic polymer precursors. For example, one patent (publication number: CN121269702A) uses sugarcane bagasse as a raw material to prepare hard carbon materials, and another patent (publication number: CN118754118B) discloses a preparation process for epoxy resin-based hard carbon. Biomass raw materials are widely available and inexpensive, but their composition and structure fluctuate greatly due to factors such as origin and season, making it difficult to control the batch consistency of the prepared hard carbon materials, affecting the uniformity and reliability of battery products. While synthetic polymer precursors have high purity and controllable structure, they are expensive, and the synthesis process may involve environmental pollution, failing to meet the requirements of green and sustainable development.

[0004] Viscose fiber is an important man-made cellulose fiber, and its production process generates a large amount of waste, including waste fibers, waste glue blocks, and filter waste. The main component of this waste is regenerated cellulose, which has advantages that natural cellulose lacks: it undergoes chemical dissolution and regenerated spinning during production, removing impurities such as lignin, resulting in high cellulose purity, regular fiber morphology, high carbon content, relatively controllable impurities, and a certain degree of molecular orientation. Currently, this type of waste is mostly treated as low-value solid waste or landfilled, causing not only resource waste but also environmental pressure. If this relatively homogeneous industrial waste could be transformed into high-value-added hard carbon anode material, it would not only achieve waste resource utilization and reduce the production cost of hard carbon but also provide a stable and high-performance anode material for sodium-ion batteries, resulting in significant economic and environmental benefits.

[0005] While there are reports of preparing hard carbon from biomass carbonization, systematic research on viscose fiber waste is still lacking. More importantly, there is a lack of systematic, efficient, and industrially feasible technical solutions for how to preserve the advantages of the fiber structure during the precursor treatment stage while optimizing the microstructure (closed-cell rate, interlayer spacing, defect concentration) of the final carbon material through process control to simultaneously obtain high capacity, high first-efficiency, and excellent rate performance. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing and applying waste viscose fiber hard carbon anode materials. This method achieves precise control over the microstructure of the material by performing structure-preserving treatment on the raw materials and combining it with a stepwise carbonization process. The resulting product possesses high reversible capacity, high first-cycle coulombic efficiency, and excellent cycle stability, while also having extremely low raw material costs, making it suitable for large-scale production. To achieve the above objectives, this invention adopts the following technical solution: This invention provides a method for preparing waste viscose fiber hard carbon material, comprising the following steps: S1: Wash and dry the waste viscose fiber to obtain the first precursor; S2: The first precursor is subjected to low-temperature heat treatment to obtain the second precursor; S3: The second precursor is carbonized at high temperature to obtain hard carbon material.

[0007] The waste viscose fiber includes one or more of the following: unshaped viscose fiber from the production process, substandard finished yarn, wastewater yarn, ordinary fiber waste yarn, high whiteness fiber waste yarn, vortex spinning waste yarn, and colored fiber waste yarn.

[0008] The water washing described in step S1 includes washing with deionized water and / or tap water.

[0009] Step S1 also includes shearing and / or pressing the dried viscose fibers into shape.

[0010] The shearing length is 0.2-2cm; the pressing pressure is 0.1-200MPa.

[0011] The low-temperature heat treatment in step S2 is performed at a temperature of 400-800℃ for a duration of 0.1-6 hours.

[0012] The heating rate for low-temperature heat treatment is 1-20℃ / min.

[0013] Step S2 also includes crushing after low-temperature heat treatment.

[0014] The crushing methods include pulverizer crushing, ball milling, or pressure crushing.

[0015] The powder after grinding and crushing has a mesh size of 50-300 mesh.

[0016] The ball milling speed is 200-1000 rpm, and the ball milling time is 0.1-4 h.

[0017] The pressure used for the pressurized crushing is 0.1-200 MPa.

[0018] The high-temperature carbonization temperature described in S3 is 1000-1600℃, and the high-temperature carbonization time is 0.5-5h.

[0019] The low-temperature heat treatment and high-temperature carbonization processes are carried out in an inert atmosphere.

[0020] The heating rate for high-temperature carbonization is 1-10℃ / min.

[0021] The present invention also provides an application of the hard carbon material obtained by the above preparation method in a sodium-ion battery, wherein the hard carbon material serves as the negative electrode of the sodium-ion battery.

[0022] Compared with the prior art, the present invention has the following advantages: (1) This invention provides a simple and low-cost method for preparing hard carbon materials. The obtained hard carbon material has a good fibrous structure, and sodium-ion batteries prepared with it as the negative electrode have excellent electrochemical performance, with outstanding reversible specific capacity, initial coulombic efficiency and cycle stability.

[0023] (2) The preparation method of hard carbon material provided by the present invention preserves the morphology of the fiber. After carbonization, a three-dimensional interconnected conductive network is naturally formed, which effectively shortens the ion / electron transport path and improves the reversible specific capacity, rate capability, cycle stability and other performance of the battery. The high purity and uniformity of viscose fiber ensure that the carbonization product has a consistent structure and controllable defects. The batch stability of the product is better than that of natural biomass. The raw material is sheared to achieve uniformity of the raw material size, which solves the problem of uneven feeding of large raw materials and uneven heat and mass transfer during carbonization. It also preserves the original morphology and axial molecular orientation of the fiber to the greatest extent, so that the carbonization product can completely inherit the three-dimensional network skeleton of the fiber. The pre-orientation of the fiber guides the orderly arrangement of carbon microcrystals, thereby obtaining an ideal electrode material with both a high conductive network and a suitable microscopic carbon structure. Press molding provides additional freedom of structural control. It can be oriented and optimized according to application requirements (high capacity or high tap density). Under pressure and high temperature, the contact points of adjacent fibers will fuse and cross-link to form a stronger carbon-carbon connection. This results in a better internal conductive network within the pulverized carbon particles and a lower interparticle contact resistance, which improves the overall conductivity of the electrode and contributes to enhanced rate performance and reversible specific capacity. A stepwise carbonization process stabilizes the framework and forms a closed-cell morphology at low temperatures, while optimizing interlayer spacing and crystallite size at high temperatures, significantly improving the material's plateau capacity and first-cycle coulombic efficiency. The material after low-temperature heat treatment is highly brittle. During crushing (e.g., ball milling, pressure crushing), mechanical forces reduce particle size, generate microcracks, and introduce numerous lattice defects and edge sites. This is equivalent to a "mechanical activation" treatment. These newly generated defects, edges, and increased specific surface area become new reaction sites during subsequent high-temperature carbonization, promoting more complex carbon structure recombination and ultimately generating richer nanopores and active sites with pseudocapacitive properties, thus contributing to improved sodium storage capacity. This invention affects the microstructure of carbon materials by changing the carbonization process. The suitable carbon layer spacing and closed-pore structure inside the hard carbon provide a large number of effective storage sites for sodium ions, exhibiting excellent reversible sodium storage specific capacity and rate performance, and realizing high-value utilization of waste.

[0024] (3) The preparation method of the hard carbon anode material provided by this invention uses waste viscose fiber as raw material. The synthesis process is simple, safe, reliable, and environmentally friendly. Compared with traditional landfill and incineration methods, this invention realizes the harmless reuse of waste viscose fiber, which can save a lot of resources, reduce CO2 emissions, and achieve sustainable development. The viscose fiber waste used in this patent has high cellulose purity and structural uniformity due to its regeneration process characteristics. After carbonization, it can obtain hard carbon material with controllable defects, less heteroatom interference, and high structural consistency. The viscose fiber raw material is easy to process, the process route is simple, and it is easy to connect with existing textile and material processing technologies. It has significant advantages in large-scale production and cost control, overcomes the key obstacles from laboratory to market, is suitable for large-scale production and practical application, and has important significance for the future commercial preparation of sodium-ion battery anodes.

[0025] (4) The hard carbon material prepared by the preparation method provided in this invention, when used as a negative electrode material for sodium-ion batteries, exhibits a reversible specific capacity as high as 300 mAh g⁻¹. -1 The capacity retention rate after 100 cycles is 96.50%. Attached Figure Description

[0026] Figure 1 This is a thermogravimetric curve image of waste high-white silk.

[0027] Figure 2 This is an XRD image of the waste viscose fiber hard carbon material prepared in Example 1.

[0028] Figure 3 This is a constant current charge-discharge curve of the first charge-discharge process of the waste viscose fiber hard carbon material prepared in Example 1.

[0029] Figure 4 This is a graph showing the 100-cycle performance of the waste viscose fiber hard carbon material prepared in Example 1.

[0030] Figure 5 This is a SEM image of the waste viscose fiber hard carbon material prepared in Example 4.

[0031] Figure 6 This is a constant current charge-discharge curve of the first charge-discharge process of the waste viscose fiber hard carbon material prepared in Comparative Example 1.

[0032] Figure 7 This is an XRD comparison chart of the raw materials in Comparative Example 2 after grinding and before grinding.

[0033] Figure 8 This is a constant current charge-discharge curve of the first charge-discharge process of the cotton stalk hard carbon material prepared in Comparative Example 3. Detailed Implementation

[0034] The present invention will be described in detail below through some representative embodiments, but the present invention is not limited to these embodiments.

[0035] Example 1 This embodiment provides a method for preparing waste viscose fiber-based hard carbon material, and the specific operation steps are as follows: Take 10g of high-whiteness waste silk, wash it with tap water, and dry it. Cut the clean waste silk into short filaments of about 0.5cm. Use a briquetting machine to press the short filaments into compact, regular blocks at a pressure of 10MPa for 5 minutes to obtain the first precursor. Place the first precursor in a carbonization furnace and perform low-temperature heat treatment under an argon atmosphere. Heat the temperature to 500℃ at a rate of 5℃ / min and hold it at this temperature for 1 hour. Then, allow it to cool naturally to room temperature to obtain the second precursor of hard carbon material. Place the second precursor in a tubular carbonization furnace for high-temperature carbonization under an argon atmosphere. Heat the temperature to 1300℃ at a rate of 5℃ / min and hold it at this temperature for 1 hour. Then, cool the temperature to 1000℃ at a rate of 2℃ / min and allow it to cool naturally to room temperature to obtain the hard carbon material. Figure 2 The XRD pattern of the hard carbon material prepared in this embodiment shows that the material exhibits an amorphous structure.

[0036] Example 2 This embodiment provides a method for preparing waste viscose fiber-based hard carbon material, and the specific operation steps are as follows: 10g of high-whiteness waste yarn was washed with tap water and dried to obtain the first precursor. The first precursor was placed in a carbonization furnace and subjected to low-temperature heat treatment under an argon atmosphere, with the temperature increased to 500℃ at a heating rate of 5℃ / min and held at this temperature for 1 hour, then allowed to cool naturally to room temperature to obtain the second precursor of the hard carbon material. The second precursor was placed in a tubular carbonization furnace for high-temperature carbonization, with the temperature increased to 1300℃ under an argon atmosphere at a heating rate of 5℃ / min and held at this temperature for 1 hour, then decreased to 1000℃ at a cooling rate of 2℃ / min, and then allowed to cool naturally to room temperature to obtain the hard carbon material.

[0037] Example 3 This embodiment provides a method for preparing waste viscose fiber-based hard carbon material, and the specific operation steps are as follows: 10g of high-whiteness waste filaments were washed with tap water, dried, and cut into short filaments of approximately 0.5cm to obtain the first precursor. The first precursor was placed in a carbonization furnace and subjected to low-temperature heat treatment under an argon atmosphere, with the temperature increased to 500℃ at a rate of 5℃ / min and held at this temperature for 1 hour. It was then allowed to cool naturally to room temperature to obtain the second precursor for hard carbon material. The second precursor was placed in a tubular carbonization furnace for high-temperature carbonization under an argon atmosphere, with the temperature increased to 1300℃ at a rate of 5℃ / min and held at this temperature for 1 hour. It was then cooled to 1000℃ at a rate of 2℃ / min and allowed to cool naturally to room temperature to obtain the hard carbon material.

[0038] Example 4 This embodiment provides a method for preparing waste viscose fiber-based hard carbon material, and the specific operation steps are as follows: 10g of high-whiteness waste filaments were washed with tap water, dried, and cut into short filaments of approximately 0.5cm to obtain the first precursor. The first precursor was placed in a carbonization furnace and subjected to low-temperature heat treatment under an argon atmosphere, heated to 500℃ at a heating rate of 5℃ / min and held at this temperature for 1 hour. It was then allowed to cool naturally to room temperature and subjected to pressure crushing using a pressure device at a pressure of 10MPa for 1 minute to obtain the second precursor. The second precursor was placed in a tubular carbonization furnace for high-temperature carbonization, heated to 1300℃ under an argon atmosphere at a heating rate of 5℃ / min and held at this temperature for 1 hour. It was then cooled to 1000℃ at a cooling rate of 2℃ / min and allowed to cool naturally to room temperature to obtain the hard carbon material. Figure 5 It can be seen that after the hard carbon material undergoes shearing pretreatment, low-temperature heat treatment, pressure crushing, and high-temperature carbonization, it still retains the morphology of the fiber structure.

[0039] Example 5 This embodiment provides a method for preparing waste viscose fiber-based hard carbon material, and the specific operation steps are as follows: 10g of high-whiteness waste filaments were washed with tap water, dried, and cut into short filaments of about 0.5cm to obtain the first precursor. The first precursor was placed in a carbonization furnace and subjected to low-temperature heat treatment under an argon atmosphere, with the temperature increased to 700℃ at a heating rate of 5℃ / min and held at this temperature for 1 hour. Then, it was allowed to cool naturally to room temperature and crushed under pressure using a pressure device at a pressure of 10MPa for 1 minute to obtain the second precursor. The second precursor was then subjected to high-temperature carbonization in a tubular carbonization furnace under an argon atmosphere, with the temperature increased to 1300℃ at a heating rate of 5℃ / min and held at this temperature for 1 hour. Then, it was allowed to cool to 1000℃ at a cooling rate of 2℃ / min and allowed to cool naturally to room temperature to obtain the hard carbon material.

[0040] Example 6 This embodiment provides a method for preparing waste viscose fiber-based hard carbon material, and the specific operation steps are as follows: 10g of wastewater filaments were washed with tap water, dried, and cut into short filaments of approximately 0.5cm to obtain the first precursor. The first precursor was placed in a carbonization furnace and subjected to low-temperature heat treatment under an argon atmosphere, with the temperature increased to 500℃ at a rate of 5℃ / min and held at this temperature for 1 hour, then allowed to cool naturally to room temperature to obtain the second precursor. The second precursor was placed in a tubular carbonization furnace for high-temperature carbonization, with the temperature increased to 1300℃ under an argon atmosphere at a rate of 5℃ / min and held at this temperature for 1 hour, then decreased to 1000℃ at a rate of 2℃ / min and allowed to cool naturally to room temperature to obtain the hard carbon material.

[0041] Comparative Example 1 10g of high-whiteness waste filaments were placed in a carbonization furnace and subjected to low-temperature heat treatment under an argon atmosphere. The temperature was increased to 500℃ at a heating rate of 5℃ / min and held at this temperature for 1 hour, then allowed to cool naturally to room temperature to obtain a hard carbon material precursor. The precursor was then placed in a tubular carbonization furnace for high-temperature carbonization under an argon atmosphere. The temperature was increased to 1300℃ at a heating rate of 5℃ / min and held at this temperature for 1 hour, then decreased to 1000℃ at a cooling rate of 2℃ / min and allowed to cool naturally to room temperature to obtain the hard carbon material.

[0042] Comparative Example 2 High-whiteness waste filaments were washed with tap water and dried. The waste filaments were then crushed using a pulverizer and sieved through a 100-mesh sieve to obtain waste filament powder. The waste filament powder was placed in a carbonization furnace and subjected to low-temperature heat treatment under an argon atmosphere. The temperature was increased to 500℃ at a rate of 5℃ / min and held at this temperature for 1 hour, then allowed to cool naturally to room temperature to obtain a hard carbon material precursor. The precursor was then placed in a tubular carbonization furnace for high-temperature carbonization under an argon atmosphere. The temperature was increased to 1300℃ at a rate of 5℃ / min and held at this temperature for 1 hour, then decreased to 1000℃ at a rate of 2℃ / min and allowed to cool naturally to room temperature to obtain the hard carbon material. Figure 7 To compare the XRD patterns of the raw materials before and after grinding, the crystallinity of the raw materials decreased from 64.3% to 50.8% after grinding, proving that grinding destroyed the fiber structure.

[0043] Comparative Example 3 Cotton stalks were washed with tap water and dried, then placed in a carbonization furnace for low-temperature heat treatment under an argon atmosphere. The temperature was increased to 500°C at a rate of 5°C / min and held at this temperature for 1 hour, followed by natural cooling to room temperature to obtain a hard carbon precursor. The precursor was then placed in a tubular carbonization furnace for high-temperature carbonization under an argon atmosphere, increased to 1300°C at a rate of 5°C / min and held at this temperature for 1 hour, followed by cooling to 1000°C at a rate of 2°C / min and then natural cooling to room temperature to obtain the hard carbon material.

[0044] Comparative Example 4 Take 10g of high-whiteness waste filaments, wash them with tap water and dry them, cut them into short filaments of about 0.5cm, and place them in a tubular carbonization furnace for high-temperature carbonization. Under an argon atmosphere, heat the furnace to 1300℃ at a heating rate of 5℃ / min, maintain this temperature for 1h, and then cool it down to 1000℃ at a cooling rate of 2℃ / min. Finally, allow it to cool naturally to room temperature to obtain hard carbon material.

[0045] Simulated battery assembly and testing The carbon materials prepared in the above examples and comparative examples were ground and mixed with CNTs and SA+PEO binder at a mass ratio of 8:1:1. An appropriate amount of pure water was added and placed in a glass bottle and stirred to form a uniformly dispersed slurry. The slurry was then coated on the current collector copper foil and vacuum dried at 100℃ for 12 hours. After drying, it was cut into round pieces with a diameter of 12 mm. The average mass load of the active material was 1.5 mg.

[0046] The simulated battery assembly was performed in an Ar atmosphere glove box, using metallic sodium as the counter electrode, 1 mol / L NaPF6 (solvent consisting of ethylene carbonate and dimethyl carbonate, volume ratio 1:1) as the electrolyte, and glass fiber filter paper as the separator. The electrode sheets from the examples and comparative examples were used as the negative electrodes to assemble CR2032 coin cells. A Neware CT4008 (Shenzhen, China) battery testing system was used, operating at a constant temperature of 30°C and 20 mAg. -1 Constant current charge-discharge tests were conducted at a given current density, with a discharge cutoff voltage of 0.01V and a charging cutoff voltage of 3V. The test results are shown in Table 1. Figure 3-4 , Figure 6 and Figure 8 As shown.

[0047] Table 1. Comparison of electrochemical performance of hard carbon materials prepared in Examples 1-6 and Comparative Examples 1-4 name Reversible specific capacity (mAh g -1 ​ Initial Coulomb efficiency (%) <![CDATA[Rate performance (2 A g -1 under) (mA h g -1 )]]> Retention rate after 100 cycles (%) Interlayer spacing (nm) Example 1 300.53 85.86 44.96 96.50 0.386 Example 2 271.47 82.06 35.94 91.09 0.379 Example 3 284.58 83.20 39.51 92.72 0.380 Example 4 294.17 84.01 40.88 94.93 0.384 Example 5 280.95 80.17 25.44 91.74 0.381 Example 6 300.88 79.82 38.68 94.51 0.386 Comparative Example 1 247.32 76.48 26.61 82.63 0.379 Comparative Example 2 255.07 69.81 5.89 76.72 0.376 Comparative Example 3 249.05 76.29 32.62 89.85 0.371 Comparative Example 4 273.18 81.29 32.73 89.02 0.381 As shown in Table 1, compared to Comparative Example 1, the high-whiteness waste fibers in Example 2, after cleaning, resulted in a hard carbon anode material with higher purity, reversible specific capacity, higher initial coulombic efficiency, and improved specific capacity under high current. This is because cleaning removes soluble impurities, surface contaminants, and some inorganic salts, making the fiber precursor purer. This helps form a more uniform carbon skeleton during carbonization and reduces interference from non-conductive impurities. Comparative Example 2 uses a strong crushing method (such as ball milling or pulverizing) to process the raw material, which completely destroys its natural fiber morphology, turning it into amorphous powder. This results in the loss of its inherent advantage as a self-supporting three-dimensional conductive network skeleton. In contrast, Examples 1-5 retain the original fiber morphology of the viscose fiber, allowing the carbonized carbon material to naturally form a three-dimensional interconnected conductive network skeleton. This structure provides a fast electron transport channel, significantly reducing the internal resistance of the electrode, thereby endowing the material with excellent reversible specific capacity, rate performance, and cycle stability. Example 4 added a pressure crushing step between the low-temperature heat treatment and high-temperature carbonization steps. The purpose is not simply to reduce size, but to intentionally introduce defects and increase specific surface area. During subsequent high-temperature carbonization, this guides the carbon structure towards an optimized closed-cell / open-cell ratio and suitable interlayer spacing, thereby significantly improving the material's reversible capacity and rate performance without sacrificing initial coulombic efficiency. Example 5 showed inferior electrochemical performance in initial coulombic efficiency and specific capacity compared to Example 4, indicating that controlling the carbonization process of viscose fibers can affect their carbonization process and thus their electrochemical performance. Example 6, using wastewater fibers as raw material, achieved good electrochemical performance under the same process conditions, demonstrating the universality of the process conditions for waste viscose fibers. When pure fibers are pressed, they form preforms with more uniform density and composition. The fibers are primarily entangled by physical forces and van der Waals forces, without interference from impurity particles. This results in more consistent heat conduction and gas diffusion during carbonization, thus making Example 1 perform better. Furthermore, compared to other biomass hard carbon anode materials prepared in Comparative Example 3, which did not achieve the performance of viscose fibers, this proves that the process route designed in this invention is specifically targeted at viscose fibers and is truly effective. Example 3 obtained a hard carbon material through stepwise carbonization, while Comparative Example 4 obtained a hard carbon material through one-step carbonization. The results show that stepwise carbonization is more advantageous for performance because: one-step carbonization simultaneously completes dehydration, depolymerization, aromatization, and carbon layer rearrangement in a continuous heating process. The various reaction stages interfere with each other, leading to violent thermal degassing and uncontrolled carbon skeleton shrinkage. The final product is prone to forming a large number of uncontrollable openings and structural defects, which restricts its first-cycle coulombic efficiency and reversible capacity as a sodium-ion battery anode. The stepwise carbonization process forms a stable primary carbon skeleton rich in aromatic structural units in the pre-carbonization stage, and in the high-temperature carbonization stage, deep aromatization and carbon layer refinement are carried out on the solidified skeleton.As can be seen, the present invention, through a stepwise carbonization process following pretreatment of waste fibers, can produce viscose fiber hard carbon anode materials with high initial discharge specific capacity, high initial coulombic efficiency, and excellent cycle performance.

[0048] The present invention has been described in detail above, with the aim of enabling those skilled in the art to understand and implement the invention. However, this description should not be construed as limiting the scope of protection of the invention. All equivalent changes or modifications made in accordance with the spirit and essence of the invention should be included within the scope of protection of the invention.

Claims

1. A method for preparing a waste viscose fiber hard carbon material, characterized in that: Includes the following steps: S1: Wash and dry the waste viscose fiber to obtain the first precursor; S2: The first precursor is subjected to low-temperature heat treatment to obtain the second precursor; S3: The second precursor is carbonized at high temperature to obtain hard carbon material.

2. The method for preparing a waste viscose fiber hard carbon material as described in claim 1, characterized in that: The waste viscose fiber includes one or more of the following: unshaped viscose fiber from the production process, substandard finished yarn, wastewater yarn, ordinary fiber waste yarn, high whiteness fiber waste yarn, vortex spinning waste yarn, and colored fiber waste yarn.

3. The method for preparing a waste viscose fiber hard carbon material as described in claim 1, characterized in that: Step S1 also includes cutting and / or pressing the dried viscose fibers into shape.

4. The method for preparing a waste viscose fiber hard carbon material as described in claim 3, characterized in that: The shearing length is 0.2-2cm; the pressing pressure is 0.1-200MPa.

5. The method for preparing a waste viscose fiber hard carbon material as described in claim 1, characterized in that: The low-temperature heat treatment in step S2 is performed at a temperature of 400-800℃ for a duration of 0.1-6 hours.

6. The method for preparing a waste viscose fiber hard carbon material as described in claim 1, characterized in that: Step S2 also includes crushing after low-temperature heat treatment.

7. The method for preparing a waste viscose fiber hard carbon material as described in claim 6, characterized in that: The crushing methods include pulverizer crushing, ball milling, or pressure crushing.

8. The method for preparing a waste viscose fiber hard carbon material as described in claim 7, characterized in that: The powder after grinding and crushing has a mesh size of 50-300 mesh; the ball milling speed is 200-1000 rpm, and the ball milling time is 0.1-4 h; the pressure of the pressurized crushing is 0.1-200 MPa.

9. The method for preparing a waste viscose fiber hard carbon material as described in claim 1, characterized in that: The high-temperature carbonization temperature in step S3 is 1000-1600℃, and the high-temperature carbonization time is 0.5-5h.

10. The application of a hard carbon material obtained by the preparation method according to any one of claims 1-9 in a sodium-ion battery, characterized in that: The hard carbon material serves as the negative electrode in a sodium-ion battery.

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