Preparation method of biomass hard carbon negative electrode material based on deep eutectic solvent treatment and application of biomass hard carbon negative electrode material in sodium-ion battery negative electrode
By treating biomass raw materials with a deep eutectic solvent, combined with microwave modification and high-temperature carbonization, a hard carbon anode material for sodium-ion batteries with high specific capacity and excellent cycle performance was prepared. This solved the problems of low process efficiency, high cost and environmental pollution in existing technologies, and realized the high added value utilization of biomass waste.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHANGSHA UNIVERSITY OF SCIENCE AND TECHNOLOGY
- Filing Date
- 2026-03-23
- Publication Date
- 2026-05-26
Smart Images
Figure CN122079129A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of sodium-ion batteries, specifically a method for preparing biomass hard carbon anode material based on deep eutectic solvent treatment and its application in sodium-ion battery anodes. Background Technology
[0002] With the continued growth of global energy demand and increasing environmental pressure, the development of green, safe, and low-cost energy storage technologies has become a research hotspot. Sodium resources are abundant and widely distributed, and sodium-ion batteries, with their advantages of low cost and high safety, are considered the most promising energy storage material to replace lithium-ion batteries. However, due to the larger radius of Na⁺ ions, traditional graphite struggles to form stable intercalation compounds. Therefore, there is a need to seek carbon materials with larger interlayer spacing and more disordered structures as anodes. Hard carbon, with its large interlayer spacing and abundant defect and pore structures, is widely recognized as one of the most promising anode materials for sodium-ion batteries.
[0003] Patent CN117208886A discloses a biomass hard carbon anode material, its preparation method, and its application. The modification method involves acid washing pretreatment combined with pre-oxidation in an air furnace at 400-550℃ for 4-6 hours, followed by pyrolysis carbonization in a nitrogen atmosphere to prepare biomass hard carbon. The pre-oxidation step takes as long as 4-6 hours, resulting in extremely low process efficiency. Acid washing only removes impurities and cannot improve the microstructure of hard carbon. The carbon interlayer spacing is not controlled, and its electrochemical performance is generally poor, with a maximum specific capacity of only 333.3 mAh / g at 0.1C.
[0004] Patent CN120191913A discloses a bamboo-based hard carbon material for sodium-ion batteries, its preparation method, and its application. Using bamboo fiber as raw material, bamboo-based hard carbon is prepared by pretreatment, pre-calcination, and high-temperature calcination with a pore-forming agent and fluoropolymer. The addition of pore-forming agents and fluoropolymers significantly increases the preparation cost and process complexity, and the use of fluoropolymers also poses an environmental burden. Pre-calcination requires 6-10 hours, and high-temperature calcination requires 4-8 hours, resulting in a long overall production cycle and low efficiency. Although carbon interlayer spacing can be controlled, nitrogen doping relies on a mixed atmosphere of NH3 and argon, requiring high atmospheric control and making industrial production difficult.
[0005] Patent CN120964768A discloses a lignocellulose biomass-based hard carbon anode material, its preparation method, and its application. It pretreats lignocellulose biomass with a hydrothermal reaction at 100-200℃ for 1-5 hours using maleic acid or other acids, followed by carbonization in an inert atmosphere to prepare the hard carbon anode material. However, the hydrothermal modification time still requires 1-5 hours, resulting in no significant improvement in process efficiency. Furthermore, the acid treatment still produces acid-containing liquid phase products, increasing the number of subsequent separation steps. The method only expands the interlayer spacing by inhibiting excessive graphite crystal growth, limiting the number of reversible sodium ion storage sites. Long-cycle performance is mediocre, with a 1 A g [value missing]. -1 The capacity retention rate was only 92% after 1500 cycles, and 5 A g -1 At high current density, the specific capacity is only 260mAh / g, and the rate performance still needs to be improved.
[0006] Patent CN117613268A discloses a lignocellulose biomass-based hard carbon anode material and its preparation method. The method involves modifying wood shavings in a water bath at 50-80℃ for 3-10 hours using a mixed solution of sodium chlorite and sodium hydroxide, followed by carbonization in an inert atmosphere to prepare lignocellulose biomass-based hard carbon. However, the sodium chlorite and sodium hydroxide mixed solution used for modification is highly corrosive, requiring sophisticated production equipment and a long modification time of 3-10 hours. Furthermore, the carbonization temperature is only 700-1000℃, resulting in insufficient carbonization, low graphitization of the hard carbon, and poor interlayer spacing control. The highest specific capacity at 0.1C is only 259.3 mAh / g, indicating limited improvement in electrochemical performance.
[0007] Existing hard carbon precursors include polymers, coal / coke, doped / composite precursors, and biomass precursors. While polymers and doped / composite precursors offer controllable structures, they are costly and involve complex processes. Coal and coke, though inexpensive, are non-renewable and contain significant amounts of ash and impurities. In contrast, biomass is widely available, renewable, and possesses a natural hierarchical porous structure and cellulose framework, making it an ideal precursor for hard carbon preparation. Research has revealed that deep eutectic solvents (DES) are novel green solvents formed by hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs) through hydrogen bonding interactions. These solvents offer advantages such as low volatility, biodegradability, and ease of preparation, exhibiting good selectivity and efficiency in biomass fractionation and lignin dissolution. Therefore, using deep eutectic solvents holds promise for controlling the microstructure of biomass precursors, thereby constructing hard carbon materials with suitable interlayer spacing and high disorder. Furthermore, this method can address the high cost and environmental pollution associated with traditional carbon material preparation methods, making it a highly significant research area. Summary of the Invention
[0008] To address the aforementioned shortcomings of existing technologies, the purpose of this invention is to propose a method for preparing biomass hard carbon anode materials based on deep eutectic solvent treatment and their application in sodium-ion battery anodes. By rapidly modifying biomass materials using a deep eutectic solvent method, a hard carbon anode material with good electrochemical performance is obtained, exhibiting high specific capacity, good rate performance, and excellent cycle stability.
[0009] To achieve the above objectives, the present invention adopts the following technical solution:
[0010] A method for preparing biomass hard carbon anode material based on deep eutectic solvent treatment includes the following steps:
[0011] (1) Pretreatment: The biomass raw material is washed with deionized water and anhydrous ethanol by ultrasonication for 0.5-2h respectively, dried at 60℃ for 8-12h, crushed and passed through a 30-50 mesh sieve to obtain biomass powder;
[0012] (2) Microwave modification with eutectic solvent: The biomass powder obtained in step (1) is placed in a microwave reactor, and DES solution is added. The solid-liquid mass-volume ratio of biomass powder to DES solution is 1:10~30. The mixture is microwave treated at 110~150℃ for 10~30 min. After filtration, washing and drying, the modified biomass precursor is obtained. DES solution is a green solvent formed by the interaction of hydrogen bond donors and hydrogen bond acceptors through hydrogen bonds.
[0013] (3) High-temperature carbonization: The modified biomass precursor obtained in step (2) is placed in a graphite crucible, heated to 1200~1400℃ in an inert protective atmosphere, calcined at a constant temperature for 2~4h, and cooled to room temperature to obtain biomass hard carbon anode material.
[0014] In the preparation method of biomass hard carbon anode material based on deep eutectic solvent treatment, in step (1), the biomass raw material is one or more of lotus stems, bamboo, and wheat straw, and the particle size of the crushed biomass powder is 30-50 mesh.
[0015] The preparation method of biomass hard carbon anode material based on deep eutectic solvent treatment, in step (2), the preparation process of DES solution is as follows: add hydrogen bond acceptor and hydrogen bond donor in a round bottom flask at a molar ratio of 1:2~20, heat and stir until the solution is clear, and cool to room temperature for later use.
[0016] In the preparation method of biomass hard carbon anode material based on deep eutectic solvent treatment, in step (2), the hydrogen bond acceptor is one or more of choline chloride, tetramethylammonium chloride, tetraethylammonium chloride, AlCl3, and ZnCl2; the hydrogen bond donor is one or more of urea, methylurea, hydrated hydrogen chloride, ethanolamine, lactic acid, anhydrous oxalic acid, glacial acetic acid, glycerol, ethylene glycol, propylene glycol, butanediol, sodium dihydrogen phosphate, glycine, alanine, and glucose.
[0017] In the preparation method of biomass hard carbon anode material based on deep eutectic solvent treatment, in step (2), the DES solution is made by mixing anhydrous oxalic acid, choline chloride and ethylene glycol in a molar ratio of 1:5:10, and the solid-liquid ratio of the crushed biomass powder to the DES solution is 1:20.
[0018] In the preparation method of biomass hard carbon anode material based on deep eutectic solvent treatment, step (2) involves washing with deionized water until neutral and drying at a temperature of 50~70℃.
[0019] In the preparation method of biomass hard carbon anode material based on deep eutectic solvent treatment, in step (3), the inert protective atmosphere is nitrogen or argon.
[0020] In the preparation method of biomass hard carbon anode material based on deep eutectic solvent treatment, step (3) involves two stages of heating: the first stage involves heating to 600-800℃ at 5-8℃ / min and holding for 0.5-2h; the second stage involves heating to 1200-1400℃ at 3-5℃ / min.
[0021] The method for preparing biomass hard carbon anode material based on deep eutectic solvent treatment, wherein the (002) interlayer spacing of the biomass hard carbon anode material is 0.36~0.39 nm, and Raman spectroscopy is performed. D / I G =1.56.
[0022] The application of a biomass hard carbon anode material based on deep eutectic solvent treatment in the anode of sodium-ion batteries involves mixing the biomass hard carbon anode material with conductive carbon black and sodium carboxymethyl cellulose at a mass ratio of 80:10:10, grinding the mixture, adding 1.2 to 1.8 times the total mass of deionized water, grinding and mixing thoroughly again to obtain a uniform slurry, coating it on aluminum foil, drying it, and cutting it into sheets to obtain a sodium-ion battery anode sheet, which is then assembled into a sodium-ion battery.
[0023] The design concept of this invention is:
[0024] This invention uses biomass such as lotus stems, bamboo, or wheat straw as a carbon source. The biomass is pretreated by washing, drying, and pulverizing to remove surface impurities. A deep eutectic solvent system composed of hydrogen bond donors and acceptors is introduced, and combined with heating and microwave-assisted treatment, lignin is selectively removed, and the crystallinity of cellulose and the microstructure of the precursor are controlled without the need for template agents, surfactants, pore-forming agents, or other auxiliary reagents. Subsequently, high-temperature carbonization is carried out in stages at 1200-1400℃ under a protective atmosphere to obtain a biomass hard carbon microstructure with suitable interlayer spacing, abundant closed-pore structure, and high disorder. Ultimately, a sodium-ion battery hard carbon anode material with high specific capacity, excellent long-cycle stability, and good rate performance is obtained, while simultaneously achieving high-value utilization of biomass waste.
[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:
[0026] 1. This invention provides a method for preparing biomass hard carbon anode materials based on deep eutectic solvent treatment. The method uses microwave-assisted deep eutectic solvent treatment to regulate the structure of biomass precursors, thereby constructing a highly disordered hard carbon microstructure for use as anode materials in sodium-ion batteries. The reaction time is short (only 10~30 min), resulting in biomass-derived hard carbon materials with good electrochemical performance. Furthermore, the DES system is a green solvent with no waste liquid pollution, meeting the requirements of green production.
[0027] 2. This invention uses natural lotus stems, bamboo or wheat straw and other biomass as raw materials. The raw materials are easy to obtain, low in cost, simple and easy to implement, and there are no templates or surfactants. It can realize large-scale industrial production and comprehensive utilization of biomass waste.
[0028] 3. The sodium-ion battery anode material prepared by the method of the present invention effectively reduces the specific surface area, increases the interlayer spacing of the carbon layers, enhances the disorder of the hard carbon material, and forms more closed pore structures and reversible sites, which is beneficial to the insertion and extraction of sodium ions.
[0029] 4. The sodium-ion battery hard carbon anode prepared by this invention has a high specific capacity, with a maximum specific capacity of 354.15 mAh g⁻¹. -1 After assembling it into a half-cell, in Ag -1 After 2000 cycles at low current density, the capacity retention is over 94%, and the average coulombic efficiency is 99.92%, with a range of 0.02~5 A g. -1 It exhibits good rate performance over a wide current density range. Attached Figure Description
[0030] Figure 1 This example demonstrates how DES solution-modulated hard carbon structures can be used as anode materials for sodium-ion batteries at potentials of 0–2.5 V and 20 mA g.-1 The charge-discharge curves at the current density.
[0031] Figure 2 This example demonstrates how DES solution modulates a hard carbon structure as a negative electrode material for sodium-ion batteries at potentials of 0–2.5 V and 1 Ag. -1 Long-cycle plot at current density.
[0032] Figure 3 This is a transmission electron microscope (TEM) image of a DES solution-modulated hard carbon structure used as a negative electrode material in a sodium-ion battery.
[0033] Figure 4 This is a Raman spectroscopy result of an example where DES solution is used to regulate the hard carbon structure as a sodium-ion battery anode material.
[0034] Figure 5 This is an X-ray diffraction pattern of a DES solution-modulated hard carbon structure used as a negative electrode material in a sodium-ion battery.
[0035] Figure 6 This example demonstrates how DES solution-modulated hard carbon structures can be used as anode materials in sodium-ion batteries at potentials of 0–2.5 V, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 3, 4, and 5 A g. -1 Rate performance diagram at current density. Detailed Implementation
[0036] In its specific implementation, this invention proposes a method for preparing biomass hard carbon anode materials based on deep eutectic solvent treatment, comprising the following steps:
[0037] (1) The pretreatment is washing, drying and crushing. The biomass is ultrasonically washed with deionized water and anhydrous ethanol for 0.5-2 h to remove impurities from the surface of the material. After ultrasonic washing, it is placed in a forced-air drying oven and dried at 60 ℃ for 8-12 h. The dried biomass powder is placed in a crusher and crushed to obtain powder. The particle size of the crushed powder is 30-50 mesh.
[0038] (2) Place the crushed powder from step (1) into a microwave reactor, add the prepared DES solution, microwave at 110~150 ℃ for 10~30 min, filter, wash and dry;
[0039] The solid-liquid mass-volume ratio (g / mL) of the crushed powder to the DES solution is 1:10~30. The DES solution is prepared by mixing hydrogen bond acceptors and hydrogen bond donors in a molar ratio of 1:2~20. The hydrogen bond donors and hydrogen bond acceptors are added to a round-bottom flask, heated and stirred until clear, and then cooled to room temperature before use.
[0040] The hydrogen bond acceptor is selected from one or more of quaternary ammonium salts (such as choline chloride, tetramethylammonium chloride, tetraethylammonium chloride, etc.) and metal halides (such as AlCl3, ZnCl2, etc.); the hydrogen bond donor is selected from one or more of ureas (such as urea, methylurea, etc.), inorganic acids (such as hydrated hydrogen chloride, etc.), ethanolamines, carboxylic acids (such as lactic acid, anhydrous oxalic acid, acetic acid, etc.), polyols (such as glycerol, ethylene glycol, propylene glycol, butylene glycol, etc.), phosphates (such as sodium dihydrogen phosphate, etc.), amino acids (such as glycine, alanine, etc.), and sugars (such as glucose, etc.).
[0041] (3) The material treated in step (2) is pyrolyzed at high temperature in a protective atmosphere such as nitrogen and argon with a graphite crucible as the carrier. The temperature is raised to 1200~1400℃ in the graphite crucible and calcined at a constant temperature for 2~4 h. After the graphite crucible is cooled to room temperature, the biomass hard carbon anode material is obtained.
[0042] The heating process is divided into two stages: the first stage involves heating at 5-8℃ / min to 600-800℃ and holding at that temperature for 0.5-2 hours; the second stage involves heating at 3-5℃ / min to 1200-1400℃.
[0043] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.
[0044] Example
[0045] In this embodiment, the preparation method of the hard carbon anode material based on deep eutectic solvent treatment of lotus stem biomass includes the following steps:
[0046] (1) Pretreatment: 2.5g of lotus stem was selected as the carbon source and washed with deionized water and anhydrous ethanol for 1 hour each. After drying at 60℃ for 10 hours, the lotus stem powder was obtained by crushing and passing through a 40-mesh sieve.
[0047] (2) Preparation of DES solution: Add anhydrous oxalic acid, choline chloride and ethylene glycol in a molar ratio of 1:5:10 to a round-bottom flask, heat and stir until clear, and cool to room temperature to obtain DES solution;
[0048] (3) Microwave modification: Place the lotus root powder in a microwave reactor, add 50 mL of the above DES solution, the solid-liquid mass-volume ratio is 1:20, microwave treat at 110℃ for 10 min, filter, wash with deionized water until neutral, and dry at 60℃ to obtain the modified lotus root precursor.
[0049] (4) High temperature carbonization: The modified lotus stem precursor was placed in a graphite crucible and heated to 800℃ at 5℃ / min and held for 1h under a nitrogen atmosphere. Then, the temperature was increased to 1400℃ at 5℃ / min and carbonized at a constant temperature for 3h. After naturally cooling to room temperature, the lotus stem-derived biomass hard carbon anode material was obtained.
[0050] (5) Electrode preparation and battery assembly: The above-mentioned hard carbon negative electrode material was mixed with conductive carbon black and sodium carboxymethyl cellulose at a mass ratio of 80:10:10. The resulting mixture was thoroughly ground in a mortar. After grinding, 1.5 times the total mass of the mixed powder was added with a pipette, and the mixture was ground and mixed thoroughly again to obtain a uniform slurry, which was then coated onto aluminum foil. After being placed in a vacuum drying oven at 60°C for 12 h to allow the solvent to evaporate completely, the slurry was cut into circular electrode sheets with a diameter of 10 mm using a cutting machine (MSK-T10), weighed, and the mass of the active material was calculated to be 0.8~0.9 mg.
[0051] Electrochemical performance testing of the hard carbon material prepared in this embodiment:
[0052] Sodium metal was used as the counter electrode, and the electrolyte was 1 mol L⁻¹. -1 A CR2032 coin cell was constructed using a diethylene glycol dimethyl ether (DEGDME) solution of NaPF6 and a glass fiber (GF / C) separator in a glove box filled with argon (Ar). The charge and discharge performance was tested using a battery testing system from Shenzhen Xinwei Electronics Co., Ltd.
[0053] like Figure 1 As shown in the charge-discharge curves of the DES solution-modified hard carbon structure as a sodium-ion battery anode material in the example, the curves exhibit typical hard carbon anode charge-discharge characteristics. After treatment, the specific capacity plateau of the curve is wider, and the maximum reversible specific capacity (approximately 354 mAh g) is higher. -1 The concentrations were significantly higher than those of the untreated sample, indicating that the DES solution with anhydrous oxalic acid, choline chloride, and ethylene glycol in a molar ratio of 1:5:10 had the most significant effect on altering the hard carbon capacity.
[0054] like Figure 2 As shown in the long-cycle diagram of the hard carbon structure regulated by DES solution as a sodium-ion battery anode material in the example, it can be seen that after 2000 cycles, the specific capacity retention rate is still above 94%, and the coulombic efficiency is stable at around 99.92%. The prepared hard carbon anode has excellent long-cycle stability and charge reversibility. Among the hard carbon materials regulated by different solutions, the DES solution with anhydrous oxalic acid, choline chloride and ethylene glycol in a molar ratio of 1:5:10 under microwave treatment has the best capacity retention rate, which solves the defect of rapid cycle decay of existing biomass hard carbon materials.
[0055] like Figures 3-5As shown, microwave treatment with a DES solution containing anhydrous oxalic acid, choline chloride, and ethylene glycol in a molar ratio of 1:5:10 significantly altered the interlayer spacing and disorder of hard carbon. X-ray diffraction (XRD) and Raman spectroscopy patterns reveal that, through controllable adjustment of the precursor carbon source composition using the DES solution, the (002) interlayer spacing of the stem-derived hard carbon material was obtained to be 0.36–0.39 nm, and the resulting derived hard carbon exhibited [missing information - likely related to I-type hard carbon]. D / I G The value was 1.56, significantly higher than the 1.47 before treatment. Combined with transmission images, it is shown that the stem-derived hard carbon prepared by this method has a high degree of disorder and a large number of closed pores. The pores are uniformly distributed and the pore size is about 2~5nm, which can effectively facilitate the insertion and extraction of sodium ions. Finally, a stem-derived hard carbon anode material for sodium-ion batteries with high capacity, high rate capability and excellent cycle performance is obtained.
[0056] like Figure 6 As shown in the rate performance graph of the DES solution-modified hard carbon structure as a sodium-ion battery anode material in the example, it can be seen that the specific capacity of the treated hard carbon at various current densities is significantly higher than that before treatment, and at 5 A g -1 The high specific capacity maintained under high current indicates that the hard carbon material with microwave-controlled DES solution of anhydrous oxalic acid, choline chloride and ethylene glycol in a molar ratio of 1:5:10 has good rate performance and can meet the application requirements of sodium-ion batteries in different power scenarios.
[0057] The results show that the hard carbon material prepared by this invention has high specific capacity and excellent cycling stability at 0.02 A g. -1 The reversible capacity at current density is significantly higher than that of the untreated sample, at 1 A g. -1 After 2000 long-cycle cycles, the capacity retention rate can reach over 94%. The method of this invention uses widely available raw materials, is low in cost, simple in process, and environmentally friendly. When using bamboo or wheat straw as carbon sources, the pretreatment, DES microwave modification, and carbonization process parameters are completely consistent with those of lotus stalks, and biomass hard carbon anode materials with comparable performance can be prepared. This enables high-value utilization of biomass waste and provides a high-performance (high capacity, high rate), low-cost, and environmentally friendly hard carbon anode material for sodium-ion batteries, which can be applied to sodium-ion battery anodes.
[0058] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.
Claims
1. A method for preparing biomass hard carbon anode material based on deep eutectic solvent treatment, characterized in that, Includes the following steps: (1) Pretreatment: The biomass raw material is washed with deionized water and anhydrous ethanol by ultrasonication for 0.5-2h respectively, dried at 60℃ for 8-12h, crushed and passed through a 30-50 mesh sieve to obtain biomass powder; (2) Microwave modification with eutectic solvent: The biomass powder obtained in step (1) is placed in a microwave reactor, and DES solution is added. The solid-liquid mass-volume ratio of biomass powder to DES solution is 1:10~30. The mixture is microwave treated at 110~150℃ for 10~30 min. After filtration, washing and drying, the modified biomass precursor is obtained. DES solution is a green solvent formed by the interaction of hydrogen bond donors and hydrogen bond acceptors through hydrogen bonds. (3) High-temperature carbonization: The modified biomass precursor obtained in step (2) is placed in a graphite crucible, heated to 1200~1400℃ in an inert protective atmosphere, calcined at a constant temperature for 2~4h, and cooled to room temperature to obtain biomass hard carbon anode material.
2. The method for preparing biomass hard carbon anode material based on deep eutectic solvent treatment according to claim 1, characterized in that, In step (1), the biomass raw material is one or more of lotus stems, bamboo, and wheat straw, and the particle size of the crushed biomass powder is 30-50 mesh.
3. The method for preparing biomass hard carbon anode material based on deep eutectic solvent treatment according to claim 1, characterized in that, In step (2), the preparation process of DES solution is as follows: add hydrogen bond acceptor and hydrogen bond donor in a round bottom flask at a molar ratio of 1:2~20, heat and stir until the solution is clear, and cool to room temperature for later use.
4. The method for preparing biomass hard carbon anode material based on deep eutectic solvent treatment according to claim 3, characterized in that, In step (2), the hydrogen bond acceptor is one or more of choline chloride, tetramethylammonium chloride, tetraethylammonium chloride, AlCl3, and ZnCl2; the hydrogen bond donor is one or more of urea, methylurea, hydrated hydrogen chloride, ethanolamine, lactic acid, anhydrous oxalic acid, glacial acetic acid, glycerol, ethylene glycol, propylene glycol, butanediol, sodium dihydrogen phosphate, glycine, alanine, and glucose.
5. The method for preparing biomass hard carbon anode material based on deep eutectic solvent treatment according to claim 3, characterized in that, In step (2), the DES solution is made by mixing anhydrous oxalic acid, choline chloride and ethylene glycol in a molar ratio of 1:5:10, and the solid-liquid ratio of the crushed biomass powder to the DES solution is 1:
20.
6. The method for preparing biomass hard carbon anode material based on deep eutectic solvent treatment according to claim 1, characterized in that, In step (2), the cleaning is done by washing with deionized water until neutral, and the drying temperature is 50~70℃.
7. The method for preparing biomass hard carbon anode material based on deep eutectic solvent treatment according to claim 1, characterized in that, In step (3), the inert protective atmosphere is nitrogen or argon.
8. The method for preparing biomass hard carbon anode material based on deep eutectic solvent treatment according to claim 1, characterized in that, In step (3), the heating process is divided into two stages: the first stage is to heat up to 600-800℃ at 5-8℃ / min and hold for 0.5-2h; the second stage is to heat up to 1200-1400℃ at 3-5℃ / min.
9. The method for preparing biomass hard carbon anode material based on deep eutectic solvent treatment according to claim 5, characterized in that, The (002) interlayer spacing of the biomass hard carbon anode material is 0.36~0.39 nm, and Raman spectroscopy test I... D / I G =1.
56.
10. The application of a biomass hard carbon anode material based on deep eutectic solvent treatment as described in any one of claims 1 to 9 in the anode of a sodium-ion battery, characterized in that, Biomass hard carbon anode material is mixed with conductive carbon black and sodium carboxymethyl cellulose at a mass ratio of 80:10:
10. After grinding, 1.2 to 1.8 times the total mass of the mixture is added to deionized water. The mixture is then ground and mixed thoroughly again to obtain a uniform slurry. This slurry is coated onto aluminum foil, dried, and cut into sheets to obtain sodium-ion battery anode sheets. The anode sheets are then assembled into sodium-ion batteries.