Lignin-based hard carbon negative electrode material with high rate performance and preparation and application thereof

Abstract

The present application belongs to the technical field of lignin hard carbon negative electrode material, and discloses a lignin-based hard carbon negative electrode material with high rate performance and a preparation and application thereof. The lignin is bridged and polymerized with long-chain bromoalkane, and then high-temperature carbonization is carried out to obtain the lignin-based hard carbon negative electrode material. The phenolic hydroxyl active sites on the lignin are used to carry out bridging polymerization reaction with long-chain bromoalkane to form a hard carbon precursor with a three-dimensional network structure of large molecular weight, long benzene ring side chain and more complex crosslinking. After carbonization, the prepared hard carbon has the characteristics of high graphitization degree, large specific surface area, long carbon layer and many closed pores, and effectively improves the specific capacity, initial coulombic efficiency and rate performance of the lignin hard carbon, and has a good practical prospect.

Description

Technical Field

[0001] This invention belongs to the technical field of lignin hard carbon anode materials, and specifically relates to a high-rate performance lignin-based hard carbon anode material and its preparation and application. Background Technology

[0002] Graphite is a commonly used anode material in lithium-ion batteries, but due to thermodynamic factors, it is difficult to form stable intercalation compounds with sodium ions, resulting in a very low sodium storage capacity. Furthermore, because the radius of sodium ions is larger than that of lithium ions, the diffusion rate of sodium ions is slow, and a large electrode volume change occurs during charge and discharge, leading to poor rate performance and cycle performance. Therefore, finding a low-cost anode material with excellent overall electrochemical performance is key to promoting the wider application of sodium-ion batteries. Hard carbon refers to carbon materials that are difficult to graphitize even at high temperatures of 2800℃. It is generally formed by sintering thermosetting precursors (oxygen-rich or hydrogen-deficient materials) such as biomass (wood, walnut shells, banana peels, etc.), sugars (glucose, sucrose, cellulose, etc.), and artificially synthesized resins at temperatures exceeding 1000℃. Hard carbon has advantages such as low cost, ease of preparation, low sodium storage potential, and high capacity, and is considered a commercially viable anode material for sodium-ion batteries. However, due to the complex structure of hard carbon and the presence of numerous pores and defects, it suffers from problems such as low initial coulombic efficiency, insufficient cycle stability, and poor rate performance. These factors severely hinder the industrial application of hard carbon anode materials.

[0003] To address these issues, researchers have proposed numerous strategies to improve the electrochemical performance of hard carbon anode materials. These strategies primarily focus on two aspects: first, microscopically controlling the pore structure and graphitization degree of hard carbon by regulating the synthesis and pyrolysis processes of the precursors. For example, Dou et al. (ChemSusChem 2017,10,2668-2676) used three biomass materials—corn cob with high hemicellulose content, peanut shell with high lignin content, and waste apple with abundant pectin content—to investigate the relationship between precursor structure and electrochemical performance. The results showed that peanut shell-based hard carbon, with lignin as the main component, possessed the highest degree of graphitization (I0.05). D / I G =0.98), the largest carbon interlayer spacing (d 002 =0.408) and the lowest specific surface area (S BET =29.8m 2 g -1 Electrochemical tests showed that the hard carbon derived from peanut shells had the highest specific capacity, at 298 mAh g⁻¹. -1 (Current density is 25 mA g) -1 ), in 1A g -1 The rate performance is 103mAh g. -1Xu et al. (Battery Energy 2023, 20220054) achieved crosslinking of two hard carbon precursors via a hydrothermal reaction of phenolic resin and sucrose, thereby enhancing the thermal stability of the phenolic resin and limiting the release of small molecules during high-temperature carbonization. The optimal crosslinking degree was achieved at a phenolic resin to sucrose mass ratio of 1:1, resulting in a hard carbon material with high graphitization, large interlayer spacing, low surface area, and low defects after carbonization at 1200℃. At 30 mA g... -1 A 323.0 mAh gg was achieved at a current density of [value missing]. -1 It has high reversible capacity and a high first-efficiency of 86.4%, and a long cycle life, but its performance in 1A g... -1 However, its rate performance is only 69.6mAh g. -1 Secondly, the degree of defects and interlayer spacing of materials can be controlled by coating and compositing with other materials, heteroatom doping, etc. Lin et al. (Adv Energy Mater, 2019, 9(1): 1803078) used three-dimensional porous graphene bulk (PGM) as model material and grew about 1 nm of Al2O3 nanoclusters on PGM defects, which significantly reduced its surface defects. In addition, the coated Al2O3 nanoclusters can inhibit the decomposition of salt in electrolyte and form a thin and uniform SEI film. Therefore, after introducing Al2O3 nanoclusters, the first efficiency, cycle stability and rate performance of PGM were greatly improved, but its reversible specific capacity was not significantly improved. Chen et al. (Journal of Materials Science & Technology, 2021, 76(17): 11-19) used starch as raw material and ammonium polyphosphate as crosslinking agent and dopant to prepare nitrogen and phosphorus co-doped porous carbon materials. The prepared carbon materials have a large specific surface area (821.88 m²). 2 g -1The graphite's abundant defect structure provides more active sites for capturing sodium ions. Furthermore, the doping of N and P atoms increases the interlayer spacing and creates a rich pore structure, increasing the sodium ion transport rate and improving rate performance. However, its initial efficiency is low (42.8%), its cycle performance is poor, and it lacks a low-voltage plateau capacity. The above analysis shows that while researchers have done a great deal of work and achieved a series of results with hard carbon materials, many problems remain. Achieving high capacity, high initial efficiency, high rate performance, and long cycle life for sodium-ion battery hard carbon anode materials remains a significant challenge. In addition, regarding raw material selection, although biomass is widely available, abundant, and inexpensive, and its original structure can be preserved after carbonization, its price fluctuates greatly due to climate or seasonal harvesting. Resin-based hard carbon allows for precise and controllable adjustment of pore structure, surface chemical composition, and active sites at the molecular level, and the prepared hard carbon exhibits good electrochemical performance; however, it is expensive and its preparation process is complex. Sugars are widely available, inexpensive, have short production cycles, and are environmentally friendly, but they have low carbon yields. Therefore, selecting suitable hard carbon precursors is crucial for the commercialization of hard carbon.

[0004] Lignin is the second most abundant natural polymer after cellulose, and the only aromatic polymer in nature with a three-dimensional network structure. Lignin macromolecules are mainly composed of three basic units: p-hydroxyphenylpropane (H), guaiacolylphenylpropane (G), and syringylphenylpropane (S), linked by various chemical bonds such as β-O-4, β-1, β-β, 4-O-5, α-O-4, 5-5′, and β-5. Industrial lignin mainly originates from pulp and paper black liquor or industrial residues from biorefining. The annual production of lignin in the paper industry is approximately 70 million tons, most of which is discarded as waste or used as low-grade fuel, causing serious environmental pollution and a significant waste of natural resources. Due to its rich functional groups, lignin is easily chemically modified, and modified lignin has seen significant development in fields such as photocatalysis, antibacterial, anti-ultraviolet, and drug sustained release. Lignin, with a carbon content as high as 60% and numerous aromatic structures in its molecules, shows great promise for the preparation of hard carbon in sodium-ion battery electrode materials after lignin modification and carbonization. Zhang et al. (ACS Applied. Material & Interfaces 2021, 13, 61180-61188) used lignin and phenolic resin as raw materials, and instantaneously formed a highly branched polymer network during the atomization process of spray drying, followed by pyrolysis to prepare hard carbon microspheres (HCMs). Compared with single precursors, combined precursors with tunable crosslinking structures more easily generate hard carbon materials with large interlayer spacing (0.399 nm) and abundant closed-pore structures by suppressing the graphitization of the precursors during carbonization. Electrochemical tests showed that HCMs exhibited high performance at 30 mA g⁻¹. -1 At a current density of 373.4 mAh g -1 It exhibits an initial reversible specific capacity and a high initial coulombic efficiency of 88%, with a capacity retention of 90.2% after 150 cycles. However, its performance at 600 mA g -1 The rate performance at current density is only 117 mAh g. -1 Chinese patent publication CN115849332A discloses a high-rate hard carbon anode material and its preparation method. This method uses a biomass polymer as a hard carbon precursor, which is mixed with anhydride-based organic compounds via a solvent method. The soft carbon properties of the anhydride-based organic compounds induce the growth of a graphite microcrystalline structure in the hard carbon and fill the open pores, forming partially closed pores to increase sodium storage capacity, thereby achieving high initial efficiency, high rate performance, and stable sodium ion storage. However, its capacity is relatively low, at 50 mA g / g. -1 The initial charge capacity at the given current density is only 243.2 mAh g. -1 .

[0005] In summary, while some of the processes described above have achieved good results in certain aspects, they are difficult to make hard carbon simultaneously achieve high initial efficiency, high capacity, high rate performance, and long cycle stability. In particular, the low capacity and poor rate performance of hard carbon at high currents limit its practical application in sodium-ion batteries. Summary of the Invention

[0006] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing a high-rate performance lignin-based hard carbon anode material.

[0007] Another objective of this invention is to provide a lignin-based hard carbon anode material with high rate performance prepared by the above method.

[0008] Another object of the present invention is to provide the application of the above-mentioned high-rate performance lignin-based hard carbon anode material in sodium-ion batteries.

[0009] The objective of this invention is achieved through the following solution:

[0010] A method for preparing a high-rate-performance lignin-based hard carbon anode material includes the following steps:

[0011] (1) Mix lignin with water, add alkali solution, heat and stir;

[0012] (2) Add a catalyst to the solution obtained in step (1), add a long-chain bromoalkane solution, heat the reaction, and cool to room temperature; wherein, long-chain bromoalkane refers to bromoalkane with a chain length of 6-12 carbons;

[0013] (3) Extraction removes the unreacted long-chain bromoalkanes from step (2), pH is adjusted, and alkyl-bridged polymerized lignin is precipitated as a hard carbon precursor.

[0014] (4) Carbonize the hard carbon precursor obtained in step (3) to obtain lignin-based hard carbon anode material.

[0015] The lignin in step (1) is one or more of alkali lignin, enzymatically hydrolyzed lignin, and organic solvent lignin.

[0016] The ratio of lignin to water in step (1) is 5-30g: 30-180mL.

[0017] The alkali in step (1) is at least one of NaOH and KOH; the mass concentration of the alkali in the alkali solution is 10%-30%, preferably 15%-25%.

[0018] The amount of alkaline solution used in step (1) is such that the pH of the solution is 10-12.

[0019] The heating and stirring in step (1) specifically involves stirring at 60-100℃ until the lignin is completely dissolved.

[0020] The catalyst in step (2) is at least one of potassium iodide, sodium iodide, magnesium iodide, and cuprous iodide.

[0021] The long-chain bromoalkane mentioned in step (2) is at least one of 1,6-dibromohexane, 1,7-dibromoheptane, 1,8-dibromooctane, 1,9-dibromononane, 1,10-dibromodecane, 1,11-dibromoundecane, and 1,12-dibromododecane; preferably at least one of 1,6-dibromohexane, 1,7-dibromoheptane, and 1,8-dibromooctane.

[0022] The solvent for the long-chain bromoalkane solution in step (2) is at least one of ethanol, acetone, glycerol, and tetrahydrofuran.

[0023] In step (2), the ratio of long-chain bromoalkane to solvent in the long-chain bromoalkane solution is 0.5-10g: 5-20mL.

[0024] The mass ratio of the catalyst, long-chain bromoalkane and lignin in step (2) is 0.1-1:0.5-10:10; preferably 0.1-0.8:0.5-8:10.

[0025] The heating reaction in step (2) is specifically carried out at 60-100℃ for 5-24 hours; preferably at 80-100℃ for 5-12 hours.

[0026] The heating reaction process described in step (2) requires the pH value of the solution to be controlled at 11-12.

[0027] The solvent used for extraction in step (3) is at least one of petroleum ether, n-hexane, and dichloromethane.

[0028] The extraction in step (3) involves 3-5 extractions, with each extraction using 50-150 mL of solvent.

[0029] In step (3), the pH is adjusted to 1-3 using sulfuric acid solution to ensure complete precipitation of the modified lignin.

[0030] The sulfuric acid solution contains 10%-50% sulfuric acid by mass.

[0031] After adjusting the pH as described in step (3), the resulting mixed solution is centrifuged, washed, dried, and ground.

[0032] The centrifugation speed is 5000-10000 rpm, and the time is 1-5 min; the drying temperature is 50-80℃.

[0033] The carbonization in step (4) involves heating to 1000-1600℃ at a rate of 1-5℃ / min under argon protection and holding for 2-6 hours.

[0034] The heating rate for carbonization in step (4) is 2-5℃ / min. -1 The carbonization time is 2-4 hours.

[0035] After carbonization in step (4), the carbonized product is cooled, washed, and dried.

[0036] The cooling is performed at a rate of 5-10°C / min to room temperature.

[0037] The washing process involves immersing the carbonized product in 0.5-2 mol / L water. -1 Stir overnight at 500-800 rpm in hydrochloric acid, then wash with water until neutral.

[0038] The drying temperature is 50-80℃; the time is 5-24h.

[0039] A lignin-based hard carbon anode material prepared by the above method.

[0040] Application of the above-mentioned lignin-based hard carbon anode material in sodium-ion batteries.

[0041] The mechanism of this invention is as follows:

[0042] Taking 1,6-dibromohexane as an example, the reaction principle is as follows:

[0043]

[0044] (1) Mix lignin with alkaline solution, heat and stir, and the pH of the solution is 10-12.

[0045] If the pH is too low in this step, the lignin will not dissolve completely; if the pH is too high, the organic reaction will not be able to occur, and the effect of lignin cross-linking cannot be achieved.

[0046] (2) Add the catalyst to the solution obtained in step (1), add the long-chain bromoalkane solution, heat the reaction, and cool to room temperature. The mass ratio of the catalyst, the long-chain bromoalkane and the lignin in step (1) is 0.1-1:0.5-10 g:10; the heating reaction is specifically carried out at 60-100℃ for 5-24 h.

[0047] The catalyst is added in this step to accelerate the chemical reaction rate. If too little catalyst is added, the reaction will be very slow; if too much is added, the reaction will be violent, with liquid splashing and the formation of other byproducts. Long chains are C6-C... 12Ideally, the carbon chain should be long enough to achieve sufficient cross-linking, resulting in low graphitization of the derived hard carbon and few closed cells. Conversely, if the carbon chain is too long, the reaction will not proceed easily. Too low a reaction temperature or too short a reaction time will result in unsatisfactory lignin cross-linking, while too high a temperature or too long a reaction time will not significantly improve lignin cross-linking but will increase energy consumption and production costs.

[0048] (3) Extract to remove unreacted long-chain bromoalkanes from step (2), adjust pH, and precipitate alkyl-bridged polymerized lignin as a hard carbon precursor. Adjust pH to 1-3 using sulfuric acid solution.

[0049] Sulfuric acid is preferred in this step, as hydrochloric acid is volatile and has a poor adjustment effect. If the pH is too high, the lignin will not precipitate completely; if the pH is too low, the increase in lignin will not be significant, but it will increase the burden of subsequent washing, making it time-consuming and labor-intensive.

[0050] (4) The hard carbon precursor obtained in step (3) is carbonized, cooled, washed, and dried to obtain lignin-based hard carbon anode material. The carbonization is carried out by heating to 1000-1600℃ at a rate of 1-5℃ / min under argon protection and holding for 2-6 hours.

[0051] This step is crucial for the carbonization and graphitization of lignin, and it must be protected with argon gas. Nitrogen gas reacts with various substances above 1000℃, resulting in incomplete carbonization and potential hazards. Lower carbonization temperatures and shorter times lead to incomplete carbonization and low graphitization levels, hindering effective sodium storage. Conversely, excessively high carbonization temperatures and longer times result in overly high graphitization levels, leading to narrow interlayer spacing, making it difficult for sodium ions to intercalate and resulting in low specific capacity.

[0052] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0053] (1) This invention utilizes the active phenolic hydroxyl sites on lignin to perform a bridging polymerization reaction with long-chain bromoalkanes to form a three-dimensional network structure hard carbon precursor with large molecular weight, long benzene ring side chains, and more complex cross-linking. The hard carbon prepared after carbonization has the characteristics of high graphitization degree, large specific surface area, long carbon layer, and many closed pores, which effectively improves the specific capacity, first coulombic efficiency, and rate performance of lignin hard carbon, and has good prospects for practical application.

[0054] (2) This invention introduces long-chain alkane small molecules into lignin macromolecules. The molecular weight and distribution of the hard carbon precursor are adjusted by regulating the ratio of lignin to long-chain brominated alkanes, the reaction time, and the temperature. The length of the lignin side chain is adjusted by regulating the carbon chain length of the long-chain brominated alkanes. The reaction is carried out under normal pressure, which is easy to operate and control.

[0055] (3) As is well known, the rate performance of hard carbon is related to the electronic conductivity of hard carbon itself and Na+ The rate of transport within hard carbon is related to its internal structure. Alkyl-bridged polymerized lignin-derived hard carbon exhibits a higher degree of graphitization, which is beneficial for improving electronic conductivity and also increases the average length (L) of short-range ordered graphite-like crystallites in hard carbon. a ) and average thickness (L c This increases the amount of Na, allowing it to store more Na. + Furthermore, the specific surface area and pore volume of modified lignin-derived hard carbon were both increased, increasing the Na+ content. + Adsorption active sites and are beneficial to Na + This improves the rate performance and reversible specific capacity of hard carbon anode materials by enhancing their transport properties. Attached Figure Description

[0056] Figure 1 The molecular weight distribution of lignin and alkyl-bridged modified lignin in Example 1 of this invention.

[0057] Figure 2 This is a high-resolution transmission electron microscope image of the hard carbon material obtained in Comparative Example 1 of the present invention.

[0058] Figure 3 This is a high-resolution transmission electron microscope image of the hard carbon material obtained in Example 1 of the present invention.

[0059] Figure 4 The X-ray diffraction patterns are those of the hard carbon materials described in Comparative Example 1 and Example 1 of the present invention.

[0060] Figure 5 The images show the Raman spectra of the hard carbon materials described in Comparative Example 1 and Example 1 of this invention.

[0061] Figure 6 This is a particle size distribution diagram of the hard carbon material described in Comparative Example 1 and Example 1 of the present invention.

[0062] Figure 7 The nitrogen adsorption-desorption curves of the hard carbon materials described in Comparative Example 1 and Example 1 of this invention are shown.

[0063] Figure 8 This is a pore size distribution diagram of the hard carbon material described in Comparative Example 1 and Example 1 of the present invention.

[0064] Figure 9 The hard carbon material described in Comparative Example 1 and Example 1 of this invention was tested at 50 mA g. -1 Cyclic performance at current density.

[0065] Figure 10 This is a rate performance diagram of the hard carbon materials described in Comparative Example 1 and Example 1 of the present invention. Detailed Implementation

[0066] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available products.

[0067] Unless otherwise specified, all reagents used in the examples are commercially available.

[0068] Example 1

[0069] (1) Weigh 10g of alkali lignin (AL) and place it in a three-necked flask. Add 50mL of deionized water and adjust the pH to 11 using 20wt% sodium hydroxide solution. Stir at 80℃ until the lignin is completely dissolved.

[0070] (2) Add 0.1g of potassium iodide to the three-necked flask in step (1), weigh 2g of 1,6-dibromohexane and dissolve it in 10mL of ethanol, and slowly add it dropwise into the three-necked flask. React at 80℃ for 5h. During the reaction, control the pH of the reaction solution to 11. After the reaction is completed, cool to room temperature.

[0071] (3) The reaction solution was repeatedly extracted with petroleum ether three times to remove the unreacted 1,6-dibromohexane in step (2). Each time, the amount of petroleum ether used was 50 mL. Then, the pH of the reaction solution was adjusted to 2 with sulfuric acid of mass concentration of 20% to completely precipitate the modified lignin. The solution was centrifuged at 10,000 rpm for 2 min, washed, dried at 80 °C, and ground to obtain alkyl-bridged polymerized lignin (AAL) as a hard carbon precursor.

[0072] (4) The precursor from step (3) was ground and added to a tube furnace. Argon gas was introduced for protection, and the temperature was raised to 1400℃ at 3℃ / min. Then, it was carbonized at a constant temperature for 2 hours and finally cooled to room temperature at a cooling rate of 5℃ / min. The carbonized product was ground and acid-washed with 1mol / L hydrochloric acid (that is, the carbonized product was immersed in 1mol / L hydrochloric acid and stirred overnight at 600rpm). It was washed with water until neutral and dried in an infrared oven at 80℃ for 12 hours to obtain alkyl-bridged polymerized lignin-based hard carbon material.

[0073] Example 2

[0074] (1) Weigh 10g of enzymatically hydrolyzed lignin and place it in a three-necked flask. Add 50mL of deionized water and adjust the pH to 11 using 20wt% sodium hydroxide solution. Stir at 90℃ until the lignin is completely dissolved.

[0075] (2) Add 0.3g of potassium iodide to the three-necked flask in step (1), weigh 5g of 1,6-dibromohexane and dissolve it in 15mL of ethanol, and slowly add it dropwise into the three-necked flask. React at 90℃ for 6h. During the reaction, control the pH of the reaction solution to 11. After the reaction is completed, cool to room temperature.

[0076] (3) The reaction solution was repeatedly extracted with petroleum ether three times to remove the unreacted 1,6-dibromohexane in step (2). The amount of petroleum ether used each time was 100 mL. Then, the pH of the reaction solution was adjusted to 2 with sulfuric acid with a mass concentration of 20% to completely precipitate the modified lignin. The solution was centrifuged at 10,000 rpm for 2 min, washed, dried at 80 °C, and ground to obtain alkyl-bridged polymerized lignin as a hard carbon precursor.

[0077] (4) The precursor from step (3) was ground and added to a tube furnace. Argon gas was introduced for protection, and the temperature was raised to 1400℃ at 3℃ / min. Then, it was carbonized at a constant temperature for 2 hours and finally cooled to room temperature at a cooling rate of 5℃ / min. The carbonized product was ground and acid-washed with 1mol / L hydrochloric acid (that is, the carbonized product was immersed in 1mol / L hydrochloric acid and stirred overnight at 600rpm). It was washed with water until neutral and dried in an infrared oven at 80℃ for 12 hours to obtain alkyl-bridged polymerized lignin-based hard carbon material.

[0078] Example 3.

[0079] (1) Weigh 10g of organic solvent lignin and place it in a three-necked flask. Add 50mL of deionized water and adjust the pH to 11 using 20wt% sodium hydroxide solution. Stir at 90℃ until the lignin is completely dissolved.

[0080] (2) Add 0.8g of potassium iodide to the three-necked flask in step (1), weigh 2g of 1,6-dibromohexane and dissolve it in 10mL of ethanol, and slowly add it dropwise into the three-necked flask. React at 90℃ for 8h. During the reaction, control the pH of the reaction solution to 11. After the reaction is completed, cool to room temperature.

[0081] (3) The reaction solution was repeatedly extracted with petroleum ether three times to remove the unreacted long-chain bromoalkanes in step (2). Each time, the amount of petroleum ether used was 50 mL. Then, the pH of the reaction solution was adjusted to 2 with sulfuric acid of mass concentration of 20% to completely precipitate the modified lignin. The solution was centrifuged at 10000 rpm for 2 min, washed, dried at 80 °C, and ground to obtain alkyl-bridged polymerized lignin as a hard carbon precursor.

[0082] (4) The precursor from step (3) was ground and added to a tube furnace. Argon gas was introduced for protection, and the temperature was raised to 1400℃ at 3℃ / min. Then, it was carbonized at a constant temperature for 2 hours and finally cooled to room temperature at a cooling rate of 5℃ / min. The carbonized product was ground and acid-washed with 1mol / L hydrochloric acid (that is, the carbonized product was immersed in 1mol / L hydrochloric acid and stirred overnight at 600rpm). It was washed with water until neutral and dried in an infrared oven at 80℃ for 12 hours to obtain alkyl-bridged polymerized lignin-based hard carbon material.

[0083] Example 4

[0084] (1) Weigh 10g of alkali lignin and place it in a three-necked flask. Add 50mL of deionized water and adjust the pH to 11 using 20wt% sodium hydroxide solution. Stir at 90℃ until the lignin is completely dissolved.

[0085] (2) Add 0.5g of potassium iodide to the three-necked flask in step (1), weigh 2g of 1,8-dibromooctane and dissolve it in 20mL of ethanol, and slowly add it dropwise into the three-necked flask. React at 90℃ for 8h. During the reaction, control the pH of the reaction solution to 11. After the reaction is completed, cool to room temperature.

[0086] (3) The reaction solution was repeatedly extracted with petroleum ether four times to remove the unreacted 1,8-dibromooctane in step (2). Each time, the amount of petroleum ether used was 100 mL. Then, the pH of the reaction solution was adjusted to 2 with sulfuric acid of mass concentration of 20% to completely precipitate the modified lignin. The solution was centrifuged at 10,000 rpm for 2 min, washed, dried at 80 °C, and ground to obtain alkyl-bridged polymerized lignin as a hard carbon precursor.

[0087] (4) The precursor from step (3) was ground and added to a tube furnace. Argon gas was introduced for protection, and the temperature was raised to 1400℃ at 3℃ / min. Then, it was carbonized at a constant temperature for 2 hours and finally cooled to room temperature at a cooling rate of 5℃ / min. The carbonized product was ground and acid-washed with 1mol / L hydrochloric acid (that is, the carbonized product was immersed in 1mol / L hydrochloric acid and stirred overnight at 600rpm). It was washed with water until neutral and dried in an infrared oven at 80℃ for 12 hours to obtain alkyl-bridged polymerized lignin-based hard carbon material.

[0088] Example 5

[0089] (1) Weigh 10g of alkali lignin and place it in a three-necked flask. Add 50mL of deionized water and adjust the pH to 11 using 20wt% sodium hydroxide solution. Stir at 100℃ until the lignin is completely dissolved.

[0090] (2) Add 0.8g of potassium iodide to the three-necked flask in step (1), weigh 2g of 1,10-dibromodecane and dissolve it in 20mL of ethanol, and slowly add it dropwise into the three-necked flask. React at 100℃ for 12h. During the reaction, control the pH of the reaction solution to 11. After the reaction is completed, cool to room temperature.

[0091] (3) The reaction solution was repeatedly extracted with petroleum ether 5 times to remove the unreacted 1,10-dibromodecane in step (2). Each time, the amount of petroleum ether used was 150 mL. Then, the pH of the reaction solution was adjusted to 2 with sulfuric acid with a mass concentration of 20% to completely precipitate the modified lignin. The solution was centrifuged at 10,000 rpm for 2 min, washed, dried at 80 °C, and ground to obtain alkyl-bridged polymerized lignin as a hard carbon precursor.

[0092] (4) The precursor from step (3) was ground and added to a tube furnace. Argon gas was introduced for protection, and the temperature was raised to 1400℃ at 3℃ / min. Then, it was carbonized at a constant temperature for 2 hours and finally cooled to room temperature at a cooling rate of 5℃ / min. The carbonized product was ground and acid-washed with 1mol / L hydrochloric acid (that is, the carbonized product was immersed in 1mol / L hydrochloric acid and stirred overnight at 600rpm). It was washed with water until neutral and dried in an infrared oven at 80℃ for 12 hours to obtain alkyl-bridged polymerized lignin-based hard carbon material.

[0093] Example 6

[0094] (1) Weigh 10g of alkali lignin and place it in a three-necked flask. Add 50mL of deionized water and adjust the pH to 11 using 20wt% sodium hydroxide solution. Stir at 80℃ until the lignin is completely dissolved.

[0095] (2) Add 0.3g of potassium iodide to the three-necked flask in step (1), weigh 5g of 1,6-dibromohexane and dissolve it in 15mL of ethanol, and slowly add it dropwise into the three-necked flask. React at 80℃ for 8h. During the reaction, control the pH of the reaction solution to 11. After the reaction is completed, cool to room temperature.

[0096] (3) The reaction solution was repeatedly extracted with petroleum ether four times to remove the unreacted 1,6-dibromohexane in step (2). Each time, the amount of petroleum ether used was 100 mL. Then, the pH of the reaction solution was adjusted to 2 with sulfuric acid of mass concentration of 20% to completely precipitate the modified lignin. The solution was centrifuged at 10,000 rpm for 2 min, washed, dried at 80 °C, and ground to obtain alkyl-bridged polymerized lignin as a hard carbon precursor.

[0097] (4) The precursor from step (3) was ground and added to a tube furnace. Argon gas was introduced for protection, and the temperature was raised to 1400℃ at 3℃ / min. Then, it was carbonized at a constant temperature for 2 hours and finally cooled to room temperature at a cooling rate of 5℃ / min. The carbonized product was ground and acid-washed with 1mol / L hydrochloric acid (that is, the carbonized product was immersed in 1mol / L hydrochloric acid and stirred overnight at 600rpm). It was washed with water until neutral and dried in an infrared oven at 80℃ for 12 hours to obtain alkyl-bridged polymerized lignin-based hard carbon material.

[0098] Example 7

[0099] (1) Weigh 10g of alkali lignin and place it in a three-necked flask. Add 50mL of deionized water and adjust the pH to 11 using 20wt% sodium hydroxide solution. Stir at 80℃ until the lignin is completely dissolved.

[0100] (2) Add 0.5g of potassium iodide to the three-necked flask in step (1), weigh 8g of 1,6-dibromohexane and dissolve it in 15mL of ethanol, and slowly add it dropwise into the three-necked flask. React at 80℃ for 12h. During the reaction, control the pH of the reaction solution to 11. After the reaction is completed, cool to room temperature.

[0101] (3) The reaction solution was repeatedly extracted with petroleum ether 5 times to remove the unreacted 1,6-dibromohexane in step (2). The amount of petroleum ether used each time was 100 mL. Then, the pH of the reaction solution was adjusted to 2 with sulfuric acid with a mass concentration of 20% to completely precipitate the modified lignin. The solution was centrifuged at 10,000 rpm for 2 min, washed, dried at 80 °C, and ground to obtain alkyl-bridged polymerized lignin as a hard carbon precursor.

[0102] (4) The precursor from step (3) was ground and added to a tube furnace. Argon gas was introduced for protection, and the temperature was raised to 1400℃ at 3℃ / min. Then, it was carbonized at a constant temperature for 2 hours and finally cooled to room temperature at a cooling rate of 5℃ / min. The carbonized product was ground and acid-washed with 1mol / L hydrochloric acid (that is, the carbonized product was immersed in 1mol / L hydrochloric acid and stirred overnight at 600rpm). It was washed with water until neutral and dried in an infrared oven at 80℃ for 12 hours to obtain alkyl-bridged polymerized lignin-based hard carbon material.

[0103] Example 8

[0104] (1) Weigh 10g of alkali lignin and place it in a three-necked flask. Add 50mL of deionized water and adjust the pH to 11 using 20wt% sodium hydroxide solution. Stir at 80℃ until the lignin is completely dissolved.

[0105] (2) Add 0.2g of potassium iodide to the three-necked flask in step (1), weigh 2g of 1,6-dibromohexane and dissolve it in 10mL of ethanol, and slowly add it dropwise into the three-necked flask. React at 80℃ for 5h. During the reaction, control the pH of the reaction solution to 11. After the reaction is completed, cool to room temperature.

[0106] (3) The reaction solution was repeatedly extracted with petroleum ether three times to remove the unreacted 1,6-dibromohexane in step (2). Each time, the amount of petroleum ether used was 50 mL. Then, the pH of the reaction solution was adjusted to 2 with sulfuric acid of mass concentration of 20% to completely precipitate the modified lignin. The solution was centrifuged at 10,000 rpm for 2 min, washed, dried at 80 °C, and ground to obtain alkyl-bridged polymerized lignin as a hard carbon precursor.

[0107] (4) The precursor from step (3) was ground and added to a tube furnace. Argon gas was introduced for protection, and the temperature was raised to 1500℃ at 2℃ / min. Then, it was carbonized at a constant temperature for 4 hours and finally cooled to room temperature at a cooling rate of 5℃ / min. The carbonized product was ground and acid-washed with 1mol / L hydrochloric acid (that is, the carbonized product was immersed in 1mol / L hydrochloric acid and stirred overnight at 600rpm). It was washed with water until neutral and dried in an infrared oven at 80℃ for 12 hours to obtain alkyl-bridged polymerized lignin-based hard carbon material.

[0108] Comparative Example 1 (Unmodified lignin hard carbon)

[0109] (1) Weigh 10g of alkali lignin and place it in a three-necked flask. Add 50mL of deionized water and adjust the pH to 11 using 20wt% sodium hydroxide solution. Stir at 80℃ until the lignin is completely dissolved and cool to room temperature.

[0110] (2) The pH of the reaction solution was adjusted to 2 with sulfuric acid of mass concentration of 20% to completely precipitate lignin. The solution was centrifuged at 10,000 rpm for 2 min, washed, dried at 80℃, and ground to obtain alkali-soluble and acid-precipitated alkali lignin as a hard carbon precursor.

[0111] (3) The precursor from step (2) was ground and added to a tube furnace. Argon gas was introduced for protection, and the temperature was raised to 1400℃ at 3℃ / min. Then, it was carbonized at a constant temperature for 2 hours and finally cooled to room temperature at a cooling rate of 5℃ / min. The carbonized product was ground and acid-washed with 1mol / L hydrochloric acid (that is, the carbonized product was immersed in 1mol / L hydrochloric acid and stirred overnight at 600rpm). It was washed with water until neutral and dried in an infrared oven at 80℃ for 12 hours to obtain lignin-based hard carbon material.

[0112] Comparative Example 2 (without catalyst)

[0113] (1) Weigh 10g of alkali lignin and place it in a three-necked flask. Add 50mL of deionized water and adjust the pH to 11 using 20wt% sodium hydroxide solution. Stir at 80℃ until the lignin is completely dissolved.

[0114] (2) Weigh 2g of 1,6-dibromohexane and dissolve it in 10mL of ethanol. Slowly add it dropwise into a three-necked flask and react at 80℃ for 5h. During the reaction, control the pH of the reaction solution to 11. After the reaction is completed, cool to room temperature.

[0115] (3) The reaction solution was repeatedly extracted with petroleum ether three times to remove the unreacted 1,6-dibromohexane in step (2). Each time, the amount of petroleum ether used was 50 mL. Then, the pH of the reaction solution was adjusted to 2 with sulfuric acid of mass concentration of 20% to completely precipitate the modified lignin. The solution was centrifuged at 10,000 rpm for 2 min, washed, dried at 80 °C, and ground to obtain alkyl-bridged polymerized lignin as a hard carbon precursor.

[0116] (4) The precursor from step (3) was ground and added to a tube furnace. Argon gas was introduced for protection, and the temperature was raised to 1400℃ at 3℃ / min. Then, it was carbonized at a constant temperature for 2 hours and finally cooled to room temperature at a cooling rate of 5℃ / min. The carbonized product was ground and acid-washed with 1mol / L hydrochloric acid (that is, the carbonized product was immersed in 1mol / L hydrochloric acid and stirred overnight at 600rpm). It was washed with water until neutral and dried in an infrared oven at 80℃ for 12 hours to obtain alkyl-bridged polymerized lignin-based hard carbon material.

[0117] Comparative Example 3 (without petroleum ether extraction)

[0118] (1) Weigh 10g of alkali lignin and place it in a three-necked flask. Add 50mL of deionized water and adjust the pH to 11 using 20wt% sodium hydroxide solution. Stir at 80℃ until the lignin is completely dissolved.

[0119] (2) Add 0.1g of potassium iodide to the three-necked flask in step (1), weigh 2g of 1,6-dibromohexane and dissolve it in 10mL of ethanol, and slowly add it dropwise into the three-necked flask. React at 80℃ for 5h. During the reaction, control the pH of the reaction solution to 11. After the reaction is completed, cool to room temperature.

[0120] (3) The pH of the reaction solution was adjusted to 2 with sulfuric acid of 20% by mass to completely precipitate the modified lignin. The solution was centrifuged at 10,000 rpm for 2 min, washed, dried at 80°C, and ground to obtain alkyl-bridged polymerized lignin as a hard carbon precursor.

[0121] (4) The precursor from step (3) was ground and added to a tube furnace. Argon gas was introduced for protection, and the temperature was raised to 1400℃ at 3℃ / min. Then, it was carbonized at a constant temperature for 2 hours and finally cooled to room temperature at a cooling rate of 5℃ / min. The carbonized product was ground and acid-washed with 1mol / L hydrochloric acid (that is, the carbonized product was immersed in 1mol / L hydrochloric acid and stirred overnight at 600rpm). It was washed with water until neutral and dried in an infrared oven at 80℃ for 12 hours to obtain alkyl-bridged polymerized lignin-based hard carbon material.

[0122] Comparative Example 4 (Carbonization temperature reduced to 1000℃)

[0123] (1) Weigh 10g of alkali lignin and place it in a three-necked flask. Add 50mL of deionized water and adjust the pH to 11 using 20wt% sodium hydroxide solution. Stir at 80℃ until the lignin is completely dissolved.

[0124] (2) Add 0.1g of potassium iodide to the three-necked flask in step (1), weigh 2g of 1,6-dibromohexane and dissolve it in 10mL of ethanol, and slowly add it dropwise into the three-necked flask. React at 80℃ for 5h. During the reaction, control the pH of the reaction solution to 11. After the reaction is completed, cool to room temperature.

[0125] (3) The reaction solution was repeatedly extracted with petroleum ether three times to remove the unreacted 1,6-dibromohexane in step (2). Each time, the amount of petroleum ether used was 50 mL. Then, the pH of the reaction solution was adjusted to 2 with sulfuric acid of mass concentration of 20% to completely precipitate the modified lignin. The solution was centrifuged at 10,000 rpm for 2 min, washed, dried at 80 °C, and ground to obtain alkyl-bridged polymerized lignin as a hard carbon precursor.

[0126] (4) The precursor from step (3) was ground and added to a tube furnace. Argon gas was introduced for protection, and the temperature was raised to 1000℃ at 3℃ / min. Then, it was carbonized at a constant temperature for 2 hours and finally cooled to room temperature at a cooling rate of 5℃ / min. The carbonized product was ground and acid-washed with 1mol / L hydrochloric acid (that is, the carbonized product was immersed in 1mol / L hydrochloric acid and stirred overnight at 600rpm). It was washed with water until neutral and dried in an infrared oven at 80℃ for 12 hours to obtain alkyl-bridged polymerized lignin-based hard carbon material.

[0127] The lignin-based hard carbon materials prepared in the above embodiments and comparative examples are used in the following applications:

[0128] First, the lignin-based hard carbon materials prepared in the examples and comparative examples were ball-milled with superconducting carbon black in a ball mill jar for 2 hours at a speed of 200 r / min. Then, the binder polyvinylidene fluoride (PVDF) was dissolved in N-methylpyrrolidone (NMP). After complete dissolution, the milled sample was transferred to the solution and stirred thoroughly for 4 hours. The mass ratio of lignin-based hard carbon material, superconducting carbon black, and PVDF was 8:1:1, and appropriate amounts of NMP were added dropwise to give the slurry a certain degree of fluidity. The slurry was coated onto copper foil using a coating applicator, dried, and then transferred to a vacuum drying oven at 110°C for 12 hours. The coated copper foil was then rolled and cut into electrode sheets with a diameter of 12 mm. The mass of each electrode sheet was weighed and recorded, and then transferred to a vacuum oven at 110°C for 12 hours. After cooling to room temperature, the electrode sheets were quickly placed in a glove box for later use. Sodium-ion batteries were assembled in a glove box filled with high-purity argon gas, with the oxygen and water content controlled to be less than 0.1 ppm during operation. In the half-cell, a sodium plate was used as the counter electrode, and a 1 mol / L NaPF6 solution (dimethyl ethylene glycol ether (DME) as the electrolyte) was used. The batteries were sequentially packaged in the following order: negative electrode shell, sodium plate, separator, electrolyte, electrode, gasket, spring contact, and positive electrode shell, assembling them into an LIR2032 coin cell for electrochemical performance testing.

[0129] The lignin-based hard carbon materials prepared in Example 1 and Comparative Example 1 were subjected to electrochemical performance testing and material characterization. The results are shown in Tables 1-3 and 1-3. Figure 1-10 .

[0130] Table 1. Graphite-like microcrystalline structure and average particle size of hard carbon in Example 1 and Comparative Example 1.

[0131]

[0132] Table 2 shows the pore structure parameters of hard carbon in Example 1 and Comparative Example 1.

[0133]

[0134] Table 3 Electrochemical performance of Examples 1-8 and Comparative Examples 1-4

[0135]

[0136] Referring to the data in Table 1, it can be seen that the hard carbon of Example 1 has a reduced interlayer spacing and an average length L of graphite-like microcrystals. a and average thickness L c As the value increases, I D with I GThe decrease in the ratio indicates that the modified lignin-based hard carbon has a higher degree of graphitization and an increased particle size. Table 2 shows that the modified lignin-based hard carbon has a larger specific surface area and pore volume, which is more conducive to sodium ion transport and electrolyte penetration, thereby shortening the sodium ion transport distance and improving its rate performance. Table 3 shows that the rate performance of the lignin-based hard carbon sodium-ion battery anode material prepared in this invention is significantly improved. In the examples, at 50 mA g... -1 After 100 cycles at the current density, the capacity retention rate was over 90%. A comparison between Example 1 and Comparative Example 1 shows that the hard carbon derived from lignin after alkyl bridging modification exhibits improved specific capacity, rate performance, and first-cycle efficiency, demonstrating superior electrochemical performance.

[0137] Figure 1 This is a molecular weight distribution diagram of lignin before and after alkyl bridging in Example 1 of the present invention. As can be seen from the diagram, the retention time of modified lignin (AAL) is shorter, indicating that its molecular weight is larger and the molecular weight distribution is narrower after modification.

[0138] Figure 2 This is a high-resolution transmission electron microscope (TEM) image of the lignin-based hard carbon material prepared in Comparative Example 1 of this invention. The image shows that the material consists of long-range disordered graphite-like microcrystals and nanopores formed by inter-crystal crosslinking, exhibiting a typical hard carbon structure. However, it has relatively few graphite-like microcrystal regions and closed pores.

[0139] Figure 3 This is a high-resolution transmission electron microscope image of the lignin-based hard carbon material prepared in Example 1 of the present invention. The image clearly shows that the carbon layer of the material is longer, and there are more graphite-like microcrystalline regions and closed pores.

[0140] Figure 4 The images show the X-ray diffraction patterns of the hard carbon described in Comparative Example 1 and Example 1 of this invention. Referring to the data in Table 1, the average length L of the modified hard carbon-like graphite crystallites is shown. a and average thickness L c The value increases significantly, and the number of graphite-like microcrystalline layers also increases, which is beneficial for sodium ion storage and electronic conductivity.

[0141] Figure 5 The images show the Raman spectra of the hard carbon described in Comparative Example 1 and Example 1 of this invention. Combined with the data in Table 1, it can be seen that the modified lignin-based hard carbon exhibits Ig... D and I G The smaller ratio indicates a higher degree of graphitization, consistent with the XRD characterization results.

[0142] Figure 6The particle size of the hard carbon described in Comparative Example 1 and Example 1 was tested using a laser particle size analyzer. According to the data in Table 1, the average particle sizes of Comparative Example 1 and Example 1 were 32.42 μm and 33.91 μm, respectively. The hard carbon particle size of Example 1 was larger because the lignin, after alkyl bridging, formed more complex cross-linked lignin macromolecules, leading to more severe agglomeration of the bridged lignin during high-temperature carbonization.

[0143] Figure 7 and Figure 8 The figures show the nitrogen adsorption-desorption curves and pore size distribution of the hard carbon described in Comparative Example 1 and Example 1 of this invention. Combined with the data in Table 2, it can be seen that the specific surface area and pore volume of the modified lignin-based hard carbon are both increased, which is beneficial for the adsorption and transport of sodium ions, thereby improving the specific capacity and rate performance of the lignin-based hard carbon.

[0144] Figure 9 Comparative Example 1 and Example 1 at 50 mA g -1 The cycling performance graph at current density shows that after 100 cycles, the specific capacity of Example 1 is 330 mAh g. -1 Higher than Comparative Example 1 (300mAh g) -1 ).

[0145] Figure 10 This is the rate performance of Comparative Example 1 and Example 1 of the present invention. As shown in the figure, Example 1 performs at 50, 100, 250, 500, and 1000 mA g. -1 The rate performance at current densities is higher than that of Comparative Example 1, especially at 1 A g. -1 Example 1 still retains 270 mAh g at current density -1 The reversible specific capacity is greater than that of Comparative Example 1, which has only 190 mAh g. -1 .

[0146] 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 a high-rate performance lignin-based hard carbon anode material for sodium-ion batteries, characterized in that... Includes the following steps: (1) Mix lignin with water, add alkali solution, heat and stir; (2) Add a catalyst to the solution obtained in step (1), add a long-chain bromoalkane solution, and heat to react; wherein, long-chain bromoalkane refers to bromoalkane with a chain length of 6-12 carbons; (3) Extraction removes the unreacted long-chain bromoalkanes from step (2), pH is adjusted, and alkyl-bridged polymerized lignin is precipitated as a hard carbon precursor. (4) Carbonize the hard carbon precursor obtained in step (3) to obtain lignin-based hard carbon anode material. The catalyst in step (2) is at least one of potassium iodide, sodium iodide, magnesium iodide, and cuprous iodide; The solvent for the long-chain bromoalkane solution in step (2) is at least one of ethanol, acetone, glycerol, and tetrahydrofuran; In step (2), the ratio of long-chain bromoalkane to solvent in the long-chain bromoalkane solution is 0.5-10g: 5-20mL; The mass ratio of the catalyst, long-chain bromoalkane, and lignin in step (2) is 0.1-1:0.5-10:10; The heating reaction process described in step (2) requires the pH value of the solution to be controlled at 11-12; In step (3), the pH is adjusted to 1-3 using sulfuric acid solution to ensure complete precipitation of the modified lignin.

2. The method for preparing the high-rate performance lignin-based hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The lignin mentioned in step (1) is one or more of alkali lignin, enzymatically hydrolyzed lignin, and organic solvent lignin; The ratio of lignin to water in step (1) is 5-30g: 30-180mL.

3. The method for preparing the high-rate performance lignin-based hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The alkali in step (1) is at least one of NaOH and KOH; the mass concentration of the alkali in the alkali solution is 10%-30%; The amount of alkaline solution used in step (1) is such that the pH of the solution is 10-12; The heating and stirring in step (1) specifically involves stirring at 60-100℃ until the lignin is completely dissolved.

4. The method for preparing the high-rate performance lignin-based hard carbon anode material for sodium-ion batteries according to claim 3, characterized in that: In step (1), the mass concentration of alkali in the alkaline solution is 15%-25%.

5. The method for preparing the high-rate performance lignin-based hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The long-chain bromoalkane mentioned in step (2) is at least one of 1,6-dibromohexane, 1,7-dibromoheptane, 1,8-dibromooctane, 1,9-dibromononane, 1,10-dibromodecane, 1,11-dibromoundecane, and 1,12-dibromododecane.

6. The method for preparing the high-rate performance lignin-based hard carbon anode material for sodium-ion batteries according to claim 5, characterized in that: The long-chain bromoalkane mentioned in step (2) is at least one of 1,6-dibromohexane, 1,7-dibromoheptane, and 1,8-dibromooctane.

7. The method for preparing the high-rate performance lignin-based hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The mass ratio of the catalyst, long-chain bromoalkane, and lignin in step (2) is 0.1-0.8:0.5-8:

10.

8. The method for preparing the high-rate performance lignin-based hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The heating reaction in step (2) is specifically carried out at 60-100℃ for 5-24 hours.

9. The method for preparing the high-rate performance lignin-based hard carbon anode material for sodium-ion batteries according to claim 8, characterized in that: The heating reaction in step (2) is specifically carried out at 80-100℃ for 5-12 hours.

10. The method for preparing the high-rate performance lignin-based hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The solvent used for extraction in step (3) is at least one of petroleum ether, n-hexane, and dichloromethane; The mass concentration of sulfuric acid in the sulfuric acid solution described in step (3) is 10%-50%; After adjusting the pH as described in step (3), the resulting mixed solution is centrifuged, washed, dried, and ground.

11. The method for preparing the high-rate performance lignin-based hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The carbonization in step (4) involves heating to 1000-1600℃ at a rate of 1-5℃ / min under argon protection and holding for 2-6 hours; after carbonization in step (4), the carbonized product is cooled, washed and dried.

12. The method for preparing the high-rate performance lignin-based hard carbon anode material for sodium-ion batteries according to claim 11, characterized in that: The heating rate for carbonization in step (4) is 2-5℃ / min. -1 The carbonization time is 2-4 hours.

13. The lignin-based hard carbon anode material prepared by the method according to any one of claims 1-12.

14. The application of the lignin-based hard carbon anode material according to claim 13 in sodium-ion batteries.

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