Lignin-based composite hard carbon material as well as preparation method and application thereof
By hydrothermal composite and high-temperature carbonization of modified lignin and nanocellulose, a multidimensional cross-linked hard carbon material was prepared, which solved the problems of complicated preparation steps and poor interfacial compatibility of lignin-based composite hard carbon materials, and achieved the improvement of high capacity and high rate performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-06
- Publication Date
- 2026-05-08
AI Technical Summary
In existing technologies, lignin-based composite hard carbon materials suffer from cumbersome preparation steps, poor interfacial compatibility, and difficulty in achieving both high capacity and high rate performance.
By dissolving lignin in a mixed solution of urea and alkali and adding a positively charged reagent, and then compounding it with nanocellulose under hydrothermal conditions to form a one-dimensional/three-dimensional cross-linked network, a multi-dimensional cross-linked hard carbon material with a large interlayer spacing was prepared through low-pressure pre-oxidation and high-temperature carbonization.
The uniform composite of lignin and cellulose was achieved, which improved the sodium storage capacity and rate performance of hard carbon materials and demonstrated excellent electrochemical performance.
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Figure CN121990558A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a lignin-based composite hard carbon material, its preparation method, and its application. Background Technology
[0002] In recent years, the price fluctuations and limited reserves of lithium resources have put enormous pressure on the future application of lithium-ion batteries (LIBs) in energy storage systems. Sodium-ion batteries (SIBs), due to their abundant sodium resources, high safety, and excellent high and low temperature performance, are considered an effective complement to LIBs. High-performance anode materials are key to the development of SIBs, with metal oxides, phosphides, organic materials, and hard carbon being the most widely studied SIB anode materials. Among them, hard carbon has advantages such as a wide range of precursor sources, high reversible capacity, and a low sodium storage potential plateau, making it the most commercially promising anode material currently available.
[0003] The sodium storage mechanism of hard carbon is mainly adsorption-filling, with the primary capacity derived from the plateau capacity created by sodium ions filling the closed pores. Therefore, increasing the closed-pore volume of hard carbon is an effective way to improve its reversible capacity. Conventional control methods (increasing carbonization temperature, template-based pore creation, etc.) can effectively increase the closed-pore volume, but the pore size inevitably increases accordingly, leading to increased microcrystal stacking, weakened sodium ion adsorption, and a decrease in rate performance. Therefore, how to control the microstructure of hard carbon to achieve both high sodium storage capacity and high rate performance has become one of the hot topics in hard carbon research.
[0004] Cellulose and lignin, among other lignin-based cellulose raw materials, are widely available and inexpensive, making them promising precursors for hard carbon. However, hard carbon structures prepared from single lignin or cellulose have limitations, making it difficult to achieve both high capacity and high rate performance. Lignin possesses a cross-linked aromatic structure, forming highly disordered amorphous carbon after carbonization. While its abundant micropores and defect sites provide considerable reversible capacity, its π-π aggregation leads to a dense lignin-based hard carbon structure, severely hindering electron conduction and ion diffusion, resulting in poor rate performance. Existing technologies have used polyaniline and polypyrrole to carbonize lignin, producing hard carbon with high capacity and rate, but the high cost of polyaniline and polypyrrole hinders large-scale production. Cellulose releases free radicals during pyrolysis, promoting closed-pore and carbon layer development, providing excellent transport channels for sodium ions, resulting in hard carbon exhibiting superior rate characteristics. However, the high crystallinity of cellulose leads to a relatively ordered microcrystalline structure in the hard carbon, limiting the formation of defect sites and resulting in lower plateau capacity and total capacity.
[0005] Regulating the composite structure of lignocellulose is an effective means to improve the sodium storage performance of hard carbon. By regulating the cross-linking and carbonization behavior during pyrolysis through intermolecular interactions, the excessive growth of hard carbon graphite microcrystals can be effectively inhibited, and the pore structure and defects can be optimized. There are two existing methods for regulating the composite structure of lignocellulose. One method involves pretreating the lignocellulose raw material to decompose the components and regulate their content. Hydrothermal pretreatment of willow branches with hydrochloric acid effectively removes hemicellulose and other impurities, but the resulting hard carbon has low capacity and rate performance, and both lignin and hemicellulose are damaged, making regulation difficult. Alternatively, hydrothermal treatment of bamboo powder with sulfuric acid effectively removes hemicellulose, resulting in hard carbon with a larger closed-pore volume and smaller closed-pore diameter, thus improving electrochemical performance. However, the hydrothermal pretreatment process is time-consuming, and lignin and cellulose inevitably degrade during hydrothermal treatment, making content difficult to control and resulting in low component utilization. The second method for regulating the composite structure of lignocellulose involves reconstructing the components of lignin, cellulose, and hemicellulose through physical mixing or chemical cross-linking. Directly mixing lignin with hemicellulose or cellulose and then carbonizing it in one step results in poor interfacial compatibility. Direct mixing cannot overcome the π-π aggregation of lignin and the hydrogen bonding between cellulose molecules, leading to significant structural differences in the resulting hard carbon and poor sodium storage performance. Alternatively, spray drying can be used to coat cellulose with ammonia-oxidized lignin. However, this process is complex, the raw materials exhibit electrostatic repulsion, coating is difficult, and improvement in interfacial compatibility is limited, resulting in poor electrochemical performance of the resulting hard carbon.
[0006] In summary, lignin-based composite hard carbon materials have the following problems as a negative electrode for sodium-ion batteries: (1) In terms of precursor preparation, acid hydrothermal pretreatment is difficult to effectively control the component content, the component utilization rate is low, and the steps are cumbersome; while direct mixing or solvent mixing of lignocellulose components cannot solve the electrostatic repulsion problem, the precursor interaction force is weak, the degree of crosslinking is low, and the interfacial compatibility is poor. (2) In terms of sodium storage performance, lignin-based composite hard carbon materials have poor overall performance, and it is difficult to balance the sodium storage specific capacity and rate performance. Summary of the Invention
[0007] In view of the above-mentioned prior art, the present invention provides a lignin-based composite hard carbon material, its preparation method and application, which solves the problems of cumbersome preparation steps, poor interface compatibility and inability to achieve both high capacity and high rate in the preparation of hard carbon materials as a negative electrode of sodium-ion batteries.
[0008] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a method for preparing a lignin-based composite hard carbon material, comprising the following steps: (1) Dissolve lignin in a mixed solution of urea and alkali to prepare a lignin solution with a concentration of 2~10 g / L, control the pH of the solution to 10~12, then add a solution containing a positively charged reagent with a concentration of 2~10 g / L, react at 80~100 ℃ for 2~6 h, and concentrate to obtain a positively charged lignin solution. (2) Add the nanocellulose dispersion to the positively charged lignin solution and hydrothermally treat it at 120~180 ℃ for 6~12 h. The resulting reaction solution is filtered and dried to obtain the lignin-nanocellulose composite precursor. (3) The lignin-nanocellulose composite precursor was pre-oxidized to obtain a highly cross-linked lignin-nanocellulose composite precursor; (4) Carbonize the highly cross-linked lignin-nanocellulose composite precursor in an inert gas to obtain lignin-based composite hard carbon material.
[0009] The beneficial effects of the above-mentioned technical solution of this invention are as follows: The method of this invention utilizes a positively charged reagent to modify alkali lignin, and then performs hydrothermal composite assembly with negatively charged nanocellulose in a urea-alkali solution to construct a uniformly composite lignin-nanocellulose precursor. Further, the cross-linking degree of the precursor is enhanced through low-pressure pre-oxidation, and then the composite precursor is placed in an inert gas atmosphere for high-temperature carbonization to obtain a lignin-based composite hard carbon material with both high capacity and high rate of change. During the preparation process, based on electrostatic interaction and esterification reaction, nanocellulose can be uniformly assembled on the lignin surface during the hydrothermal process, forming a one-dimensional / three-dimensional cross-linked network, breaking the hydrogen bonding between cellulose molecular chains and the π-π aggregation between lignin molecules. After low-pressure pre-oxidation, the composite precursor can inhibit the orderly stacking of carbon layers in the subsequent high-temperature carbonization process, expand the carbon layer spacing, increase the closed-pore structure, and form a composite hard carbon with a multi-dimensional cross-linked structure, large interlayer spacing, and abundant graphite-like microcrystals.
[0010] Based on the above technical solution, the present invention can be further improved as follows.
[0011] Furthermore, the lignin is at least one of the following: pine alkali lignin, reed alkali lignin, bamboo alkali lignin, wheat straw alkali lignin, and corn cob alkali lignin; the alkali is at least one of the following: sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate; and the positively charged reagent is at least one of the following: hexadecyltrimethylammonium chloride, alkyldimethylbenzylammonium chloride, dicedyldimethylammonium chloride, and methyltributylammonium chloride.
[0012] Furthermore, the mass ratio of lignin:urea:alkali:positively charged reagent:nanocellulose is 100:10~50:20~100:20~100:20~200.
[0013] Furthermore, the mass ratio of lignin:urea:alkali:positively charged reagent:nanocellulose is 100:10~30:20~60:30~80:50~120.
[0014] Further, the concentration is achieved through heating at 80–100 °C, resulting in a positively charged lignin solution with a concentration of 30–50 wt%. The beneficial effects of the above-mentioned further technical solutions of the present invention are as follows: If only urea solution is used to dissolve lignin, the lignin will not be completely dissolved; if only alkaline solution is used, the hydrogen bond network between cellulose molecules cannot be fully opened in step (2). If the concentration of the lignin solution is too high, the grafting efficiency of the positively charged groups will be inhibited; if the concentration of the lignin solution is too low, the yield of the positively charged lignin will be affected. If the concentration of the positively charged reagent is too low, the reaction temperature is too low, or the reaction time is too short, the positive charge modification of lignin will be incomplete, affecting the composite of lignin and negatively charged nanocellulose in step (2); if the concentration of the positively charged reagent is too high, the reaction temperature is too high, or the reaction time is too long, the preparation cost will increase. The concentration of the concentrate needs to be controlled at 30~50 wt% during the concentration process. Too high or too low a concentration is not conducive to the composite with nanocellulose in step (2).
[0015] Furthermore, the concentration of the nanocellulose dispersion is 2-6 wt%; the nanocellulose is at least one of the following: nanocellulose prepared by mechanical method, carboxyl nanocellulose prepared by Tempo oxidation method, carboxylated nanocellulose prepared by etherification method, and carboxyl nanocellulose nanocrystals prepared by acid hydrolysis method, with a diameter of 10-30 nm and a length of 1-20 μm.
[0016] Furthermore, the hydrothermal treatment is carried out in a blower oven using a hydrothermal autoclave as the container, and the drying is performed by vacuum drying, infrared drying, or freeze drying.
[0017] The beneficial effects of the above-mentioned further technical solutions of the present invention are as follows: if the concentration of the nanocellulose dispersion is too low, it will affect the composite efficiency with lignin; if the concentration of the nanocellulose dispersion is too high, the composite of lignin and nanocellulose will be uneven. If the amount of nanocellulose is too low, a one-dimensional / three-dimensional cross-linked lignin-nanocellulose composite precursor cannot be formed; if the amount of nanocellulose is too high, it will affect the particle size of the composite hard carbon material in step (4). Hydrothermal treatment is to enhance the electrostatic adsorption of positively charged lignin and negatively charged nanocellulose, and to induce esterification cross-linking between lignin hydroxyl groups and cellulose carboxyl groups. If the hydrothermal temperature is too high or the time is too long, it will cause the nanocellulose to degrade, affecting the yield of the composite precursor; if the hydrothermal temperature is too low or the time is too short, it will result in a low degree of composite between lignin and nanocellulose.
[0018] Furthermore, pre-oxidation is carried out using a flat vulcanizing machine, with a pre-oxidation pressure of 0.1~1 MPa, a pre-oxidation temperature of 150~250 ℃, and a pre-oxidation time of 0.5~4 h; the carbonization temperature is 1000~1500 ℃, the carbonization time is 3~6 h, the heating rate is 2~5 ℃ / min, and the inert gas is nitrogen or argon.
[0019] The beneficial effects of the above-mentioned further technical solutions of the present invention are as follows: If the pre-oxidation pressure is too high, the composite hard carbon material obtained in step (4) will have a dense structure, affecting the sodium storage performance; if the pressure is too low, the degree of cross-linking of the composite precursor will be low; if the temperature is too low or the time is too short, cross-linking cannot be generated; if the temperature is too high or the time is too long, lignin and nanocellulose will decompose, reducing the yield of the hard carbon material in step (4). If the carbonization temperature is too low or the carbonization time is too short, the specific surface area of the hard carbon will be large and the number of graphite-like microcrystals will be small, affecting the sodium storage capacity; if the carbonization temperature is too high or the time is too short, the hard carbon graphite microcrystals will grow excessively, the interlayer spacing will become smaller, and the sodium storage performance will decrease; if the heating rate is too slow, the hard carbon layers will grow in an orderly manner and the disorder degree will be low; if the heating rate is too fast, the carbonization will be incomplete, which is not conducive to the formation of a graphite-like microcrystal structure.
[0020] Furthermore, the lignin-based composite hard carbon material prepared by the above-mentioned method is a lignin-based composite hard carbon material.
[0021] Furthermore, the above-mentioned lignin-based composite hard carbon material is used in sodium-ion battery anode materials.
[0022] The beneficial effects of the above-mentioned further technical solutions of the present invention are as follows: the method of the present invention can enhance the interfacial compatibility of lignin and cellulose, and achieve uniform composite of the two; the prepared hard carbon has multidimensional cross-linking characteristics, large interlayer spacing and abundant graphite-like microcrystals in structure; this hard carbon material has high reversible capacity and excellent rate performance when applied in sodium-ion battery energy storage.
[0023] The beneficial effects of the present invention are: (1) The present invention promotes the uniform composite assembly of lignin and nanocellulose by means of electrostatic interaction and esterification reaction, forming a one-dimensional / three-dimensional cross-linked network, which inhibits the problem of carbon layer shrinkage and stacking during the carbonization process of lignin and cellulose, and effectively regulates the structural characteristics of lignin-based composite hard carbon. (2) The lignin-based composite hard carbon material prepared by the present invention has a multi-dimensional cross-linked structure, large interlayer spacing and abundant graphite-like microcrystals. As a negative electrode material for sodium-ion batteries, it can simultaneously improve sodium storage capacity and rate capability, and exhibits excellent electrochemical performance. Attached Figure Description
[0024] Figure 1 Here is a SEM image of the lignin-nanocellulose composite precursor prepared in Example 1; Figure 2This is a TEM image of the lignin-based composite hard carbon material prepared in Example 1; Figure 3 The XRD test comparison diagrams of the lignin-based composite hard carbon materials obtained in Example 1 and Comparative Examples 1-4 are shown. Figure 4 The first charge-discharge curves of the lignin-based composite hard carbon materials prepared in Example 1 and Comparative Examples 1-4 as anode materials for sodium-ion batteries are shown below. Figure 5 The rate performance curves of the lignin-based composite hard carbon materials prepared in Example 1 and Comparative Examples 1-4 as anode materials for sodium-ion batteries at different current densities are shown. Detailed Implementation
[0025] The specific embodiments of the present invention will be described in detail below with reference to examples.
[0026] Example 1 A lignin-based composite hard carbon material is prepared by the following steps: (1) Prepare a 1000 mL lignin solution with a concentration of 10 g / L by mixing 10 g of purified pine alkali lignin, 2 g of urea and 4 g of sodium hydroxide. Control the pH of the solution to 11. Then add 1000 mL of cetyltrimethylammonium chloride with a concentration of 5 g / L. After reacting at 90 °C for 3 h, concentrate the solution at 90 °C until the mass fraction of the concentrate is 40 wt% to obtain a positively charged lignin solution.
[0027] (2) 160 g of a 6 wt% mechanically prepared nanocellulose dispersion (nanocellulose with a diameter of 10~30 nm and a length of 1~20 μm) was added to the above positively charged lignin solution. After stirring at 1000 rpm for 1 h, the mixture was transferred to a hydrothermal reactor and placed in a forced-air oven at 160 ℃ for 8 h. After cooling to room temperature, the reaction solution was filtered until the filtrate was neutral. The obtained solid was freeze-dried and then ground to obtain the lignin-nanocellulose composite precursor.
[0028] (3) The composite precursor was placed in a flat vulcanizing machine with a pressure of 0.2 MPa and a temperature of 180 °C. After pre-oxidation for 2 h, a highly cross-linked lignin-nanocellulose composite precursor was obtained.
[0029] (4) The highly cross-linked lignin-nanocellulose composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1300 ℃ at a rate of 2.5 ℃ / min and held for 4 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based composite hard carbon material.
[0030] Example 2 A lignin-based composite hard carbon material is prepared by the following steps: (1) Prepare a 1000 mL lignin solution with a concentration of 10 g / L by mixing 10 g of purified reed alkaloid lignin, 2 g of urea and 4 g of sodium hydroxide. Control the pH of the solution to 11. Then add 1000 mL of alkyl dimethyl benzyl ammonium chloride with a concentration of 5 g / L. After reacting at 90 °C for 3 h, concentrate the solution at 90 °C until the mass fraction of the concentrate is 40 wt% to obtain a positively charged lignin solution.
[0031] (2) 160 g of a 4 wt% carboxyl nanocellulose dispersion (nanocellulose with a diameter of 10~30 nm and a length of 1~20 μm) prepared by Tempo oxidation was added to the above positively charged lignin solution. After stirring at 1000 rpm for 1 h, the mixture was transferred to a hydrothermal reactor and placed in a forced-air oven at 160 ℃ for 8 h. After cooling to room temperature, the reaction solution was filtered until the filtrate was neutral. The obtained solid was freeze-dried and then ground to obtain the lignin-nanocellulose composite precursor.
[0032] (3) The composite precursor was placed in a flat vulcanizing machine with a pressure of 0.5 MPa and a temperature of 180 °C. After pre-oxidation for 1 h, a highly cross-linked lignin-nanocellulose composite precursor was obtained.
[0033] (4) The highly cross-linked lignin-nanocellulose composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1300 ℃ at a rate of 2.5 ℃ / min and held for 4 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based composite hard carbon material.
[0034] Example 3 A lignin-based composite hard carbon material is prepared by the following steps: (1) Prepare a 1000 mL lignin solution with a concentration of 10 g / L by mixing 10 g of purified bamboo alkaloid lignin, 2 g of urea and 4 g of potassium hydroxide. Control the pH of the solution to 11. Then add 1000 mL of methyltributylammonium chloride with a concentration of 5 g / L. After reacting at 90 °C for 2 h, concentrate the solution at 90 °C until the mass fraction of the concentrate is 40 wt% to obtain a positively charged lignin solution.
[0035] (2) 200 g of carboxylated nanocellulose dispersion (nanocellulose diameter of 10~30 nm and length of 1~20 μm) prepared by etherification method with a concentration of 4 wt% was added to the above positively charged lignin solution. After stirring at 1000 rpm for 1 h, it was transferred to a hydrothermal reactor and placed in a forced-air drying oven at 160 ℃ for 12 h. After cooling to room temperature, the reaction solution was filtered until the filtrate was neutral. The obtained solid was dried by infrared drying and then ground to obtain the lignin-nanocellulose composite precursor.
[0036] (3) The composite precursor was placed in a flat vulcanizing machine with a pressure of 0.2 MPa and a temperature of 200 °C. After pre-oxidation for 2 h, a highly cross-linked lignin-nanocellulose composite precursor was obtained.
[0037] (4) The highly cross-linked lignin-nanocellulose composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under an argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1400 ℃ at a rate of 2.5 ℃ / min, and held for 3 h. After naturally cooling to room temperature, the carbonized product was ball-milled in a high-speed swing array ball mill for 5 min to obtain lignin-based composite hard carbon material.
[0038] Example 4 A lignin-based composite hard carbon material is prepared by the following steps: (1) Prepare a 1000 mL lignin solution with a concentration of 10 g / L by mixing 10 g of purified wheat straw lignin, 2 g of urea and 4 g of sodium carbonate. Control the pH of the solution to 11. Then add 1000 mL of cetyltrimethylammonium chloride with a concentration of 5 g / L. After reacting at 90 °C for 6 h, concentrate the solution at 90 °C until the mass fraction of the concentrate is 40 wt% to obtain a positively charged lignin solution.
[0039] (2) 250 g of a 2 wt% acid hydrolysis solution of carboxylated nanocellulose nanocrystals (nanocellulose with a diameter of 10~30 nm and a length of 1~20 μm) was added to the above positively charged lignin solution. After stirring at 1000 rpm for 1 h, the solution was transferred to a hydrothermal reactor and placed in a forced-air oven at 160 ℃ for 8 h. After cooling to room temperature, the reaction solution was filtered until the filtrate was neutral. The resulting solution was freeze-dried in infrared and then ground to obtain the lignin-nanocellulose composite precursor.
[0040] (3) The composite precursor was placed in a flat vulcanizing machine with a pressure of 0.3 MPa and a temperature of 160 °C. After pre-oxidation for 4 h, a highly cross-linked lignin-nanocellulose composite precursor was obtained.
[0041] (4) The highly cross-linked lignin-nanocellulose composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1200 ℃ at a rate of 2.5 ℃ / min and held for 4 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based composite hard carbon material.
[0042] Example 5 A lignin-based composite hard carbon material is prepared by the following steps: (1) Prepare a 1000 mL lignin solution with a concentration of 10 g / L by mixing 10 g of purified pine alkali lignin, 3 g of urea and 2 g of sodium bicarbonate. Control the pH of the solution to 11. Add 1000 mL of cetyltrimethylammonium chloride with a concentration of 6 g / L. After reacting at 80 °C for 6 h, concentrate the solution at 80 °C until the mass fraction of the concentrate is 40 wt% to obtain a positively charged lignin solution.
[0043] (2) 200 g of a 6 wt% mechanically prepared nanocellulose dispersion (nanocellulose with a diameter of 10~30 nm and a length of 1~20 μm) was added to the above positively charged lignin solution. After stirring at 1000 rpm for 1 h, the mixture was transferred to a hydrothermal reactor and placed in a forced-air oven at 160 ℃ for 8 h. After cooling to room temperature, the reaction solution was filtered until the filtrate was neutral. The obtained solid was dried under vacuum and then ground to obtain the lignin-nanocellulose composite precursor.
[0044] (3) The composite precursor was placed in a flat vulcanizing machine with a pressure of 1 MPa and a temperature of 180 °C. After pre-oxidation for 1 h, a highly cross-linked lignin-nanocellulose composite precursor was obtained.
[0045] (4) The highly cross-linked lignin-nanocellulose composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1500 ℃ at a rate of 2.5 ℃ / min and held for 3 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based composite hard carbon material.
[0046] Example 6 A lignin-based composite hard carbon material is prepared by the following steps: (1) Prepare a 1000 mL lignin solution with a concentration of 10 g / L by mixing 10 g of purified corn cob alkali lignin, 1 g of urea and 6 g of sodium hydroxide. Control the pH of the solution to 11. Add 1000 mL of cetyltrimethylammonium chloride with a concentration of 2 g / L. After reacting at 100 °C for 3 h, concentrate the solution at 100 °C until the mass fraction of the concentrate is 40 wt% to obtain a positively charged lignin solution.
[0047] (2) 500 g of a 2 wt% mechanically prepared nanocellulose dispersion (nanocellulose with a diameter of 10~30 nm and a length of 1~20 μm) was added to the above positively charged lignin solution. After stirring at 1000 rpm for 1 h, the mixture was transferred to a hydrothermal reactor and placed in a forced-air oven at 120 ℃ for 8 h. After cooling to room temperature, the reaction solution was filtered until the filtrate was neutral. The obtained solid was freeze-dried and then ground to obtain the lignin-nanocellulose composite precursor.
[0048] (3) The composite precursor was placed in a flat vulcanizing machine with a pressure of 0.3 MPa and a temperature of 180 °C. After pre-oxidation for 3 h, a highly cross-linked lignin-nanocellulose composite precursor was obtained.
[0049] (4) The highly cross-linked lignin-nanocellulose composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1300 ℃ at a rate of 2.5 ℃ / min and held for 4 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based composite hard carbon material.
[0050] Example 7 A lignin-based composite hard carbon material is prepared by the following steps: (1) Prepare a 1000 mL lignin solution with a concentration of 2 g / L by mixing 2 g of purified corn cob alkali lignin, 1 g of urea and 2 g of sodium hydroxide. Control the pH of the solution to 11. Add 1000 mL of 8 g / L decyl dimethyl ammonium chloride. After reacting at 90 °C for 3 h, concentrate the solution at 100 °C until the mass fraction of the concentrate is 50 wt% to obtain a positively charged lignin solution.
[0051] (2) 100 g of a 2 wt% mechanically prepared nanocellulose dispersion (nanocellulose with a diameter of 10~30 nm and a length of 1~20 μm) was added to the above positively charged lignin solution. After stirring at 1000 rpm for 1 h, the mixture was transferred to a hydrothermal reactor and placed in a forced-air oven at 180 ℃ for 6 h. After cooling to room temperature, the reaction solution was filtered until the filtrate was neutral. The obtained solid was freeze-dried and then ground to obtain the lignin-nanocellulose composite precursor.
[0052] (3) The composite precursor was placed in a flat vulcanizing machine with a pressure of 0.3 MPa and a temperature of 250 °C. After pre-oxidation for 3 h, a highly cross-linked lignin-nanocellulose composite precursor was obtained.
[0053] (4) The highly cross-linked lignin-nanocellulose composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1300 ℃ at a rate of 2.5 ℃ / min and held for 4 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based composite hard carbon material.
[0054] Example 8 A lignin-based composite hard carbon material is prepared by the following steps: (1) Prepare a 2000 mL lignin solution with a concentration of 5 g / L by mixing 10 g of purified corn cob alkali lignin, 3 g of urea and 2 g of sodium hydroxide. Control the pH of the solution to 11. Add 1000 mL of cetyltrimethylammonium chloride with a concentration of 10 g / L. After reacting at 80 °C for 5 h, concentrate the solution at 100 °C until the mass fraction of the concentrate is 30 wt% to obtain a positively charged lignin solution.
[0055] (2) 400 g of a 5 wt% mechanically prepared nanocellulose dispersion (nanocellulose with a diameter of 10~30 nm and a length of 1~20 μm) was added to the above positively charged lignin solution. After stirring at 1000 rpm for 1 h, the mixture was transferred to a hydrothermal reactor and placed in a forced-air oven at 160 ℃ for 12 h. After cooling to room temperature, the reaction solution was filtered until the filtrate was neutral. The obtained solid was freeze-dried and then ground to obtain the lignin-nanocellulose composite precursor.
[0056] (3) The composite precursor was placed in a flat vulcanizing machine with a pressure of 0.3 MPa and a temperature of 180 °C. After pre-oxidation for 3 h, a highly cross-linked lignin-nanocellulose composite precursor was obtained.
[0057] (4) The highly cross-linked lignin-nanocellulose composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1300 ℃ at a rate of 2.5 ℃ / min and held for 6 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based composite hard carbon material.
[0058] Comparative Example 1 A lignin-based hard carbon material is prepared as follows (compared to Example 1, the lignin is not positively charged): (1) 10 g of purified pine alkali lignin, 2 g of urea and 4 g of sodium hydroxide were prepared into 1000 mL of lignin solution with a concentration of 10 g / L. 500 g of 2 wt% mechanically prepared nanocellulose dispersion (nanocellulose with a diameter of 10~30 nm and a length of 1~20 μm) was added to the above lignin solution. After stirring at 1000 rpm for 1 h, the mixture was transferred to a hydrothermal reactor and placed in a forced-air drying oven at 160 ℃ for 8 h. After cooling to room temperature, the reaction solution was filtered until the filtrate was neutral. The obtained solid was freeze-dried and then ground to obtain the lignin-nanocellulose composite precursor.
[0059] (2) The composite precursor was placed in a flat vulcanizing machine with a pressure of 0.2 MPa and a temperature of 180°C. After pre-oxidation for 2 hours, the cross-linked lignin-nanocellulose composite precursor was obtained.
[0060] (3) The cross-linked lignin-nanocellulose composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1300 ℃ at a rate of 2.5 ℃ / min and held for 4 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based composite hard carbon material.
[0061] Comparative Example 2 A lignin-based hard carbon material is prepared as follows (compared to Example 1, lignin is not combined with nanocellulose): (1) Prepare a 1000 mL lignin solution with a concentration of 10 g / L by mixing 10 g of purified pine alkali lignin, 2 g of urea and 4 g of sodium hydroxide. Control the pH of the solution to 11. Then add 1000 mL of cetyltrimethylammonium chloride with a concentration of 5 g / L. After reacting at 90 °C for 3 h, concentrate the solution at 90 °C until the mass fraction of the concentrate is 40 wt% to obtain a positively charged lignin solution.
[0062] (2) The above positively charged lignin solution was freeze-dried and then ground to obtain a lignin precursor. The precursor was placed in a flat vulcanizing machine with a pressure of 0.2 MPa and a temperature of 180°C and pre-oxidized for 2 h to obtain a pre-oxidized lignin precursor.
[0063] (3) The pre-oxidized lignin precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1300 ℃ at a rate of 2.5 ℃ / min and held for 4 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based hard carbon material.
[0064] Comparative Example 3 A lignin-based hard carbon material is prepared as follows (compared to Example 1, the lignin solution and nanocellulose dispersion are not subjected to hydrothermal treatment): (1) Prepare a 1000 mL lignin solution with a concentration of 10 g / L by mixing 10 g of purified pine alkali lignin, 2 g of urea and 4 g of sodium hydroxide. Control the pH of the solution to 11. Add 1000 mL of cetyltrimethylammonium chloride with a concentration of 5 g / L. After reacting at 90 °C for 3 h, concentrate the solution at 90 °C until the mass fraction of the concentrate is 40 wt% to obtain a positively charged lignin solution.
[0065] (2) 500 g of a 2 wt% mechanically prepared nanocellulose dispersion (nanocellulose with a diameter of 10~30 nm and a length of 1~20 μm) was added to the above positively charged lignin solution. After stirring at 1000 rpm for 1 h, the mixture was filtered until the filtrate was neutral. The obtained solid was freeze-dried and then ground to obtain the lignin-nanocellulose composite precursor.
[0066] (3) The composite precursor was placed in a flat vulcanizing machine with a pressure of 0.2 MPa and a temperature of 180 °C. After pre-oxidation for 2 h, a highly cross-linked lignin-nanocellulose composite precursor was obtained.
[0067] (4) The highly cross-linked lignin-nanocellulose composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1300 ℃ at a rate of 2.5 ℃ / min and held for 4 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based composite hard carbon material.
[0068] Comparative Example 4 A lignin-based hard carbon material is prepared as follows (compared to Example 1, the lignin-nanocellulose composite precursor is not pre-oxidized): (1) Prepare a 1000 mL lignin solution with a concentration of 10 g / L by mixing 10 g of purified pine alkali lignin, 2 g of urea and 4 g of sodium hydroxide. Control the pH of the solution to 11. Then add 1000 mL of cetyltrimethylammonium chloride with a concentration of 5 g / L. After reacting at 90 °C for 3 h, concentrate the solution at 90 °C until the mass fraction of the concentrate is 40 wt% to obtain a positively charged lignin solution.
[0069] (2) 500 g of a 2 wt% mechanically prepared nanocellulose dispersion (nanocellulose with a diameter of 10~30 nm and a length of 1~20 μm) was added to the above positively charged lignin solution. After stirring at 1000 rpm for 1 h, the mixture was transferred to a hydrothermal reactor and placed in a forced-air oven at 160 ℃ for 8 h. After cooling to room temperature, the reaction solution was filtered until the filtrate was neutral. The obtained solid was freeze-dried and then ground to obtain the lignin-nanocellulose composite precursor.
[0070] (3) The lignin-nanocellulose composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1300 ℃ at a rate of 2.5 ℃ / min and held for 4 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based composite hard carbon material.
[0071] Comparative Example 5 A lignin-based hard carbon material is prepared as follows (compared to Example 1, the nanocellulose dispersion is replaced with micron-sized cellulose powder): (1) Prepare a 1000 mL lignin solution with a concentration of 10 g / L by mixing 10 g of purified pine alkali lignin, 2 g of urea and 4 g of sodium hydroxide. Control the pH of the solution to 11. Add 1000 mL of cetyltrimethylammonium chloride with a concentration of 5 g / L. After reacting at 90 °C for 3 h, concentrate the solution at 90 °C until the mass fraction of the concentrate is 40 wt% to obtain a positively charged lignin solution.
[0072] (2) 10 g of micron-sized cellulose powder was added to the above positively charged lignin solution. After stirring at 1000 rpm for 1 h, the mixture was transferred to a hydrothermal reactor and placed in a forced-air oven at 160 ℃ for 8 h. After cooling to room temperature, the reaction solution was filtered until the filtrate was neutral. The obtained solid was freeze-dried and then ground to obtain the lignin-cellulose powder composite precursor.
[0073] (3) The composite precursor was placed in a flat vulcanizing machine with a pressure of 0.2 MPa and a temperature of 180 °C. After pre-oxidation for 2 h, the cross-linked lignin-cellulose powder composite precursor was obtained.
[0074] (4) The cross-linked lignin-cellulose powder composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1300 ℃ at a rate of 2.5 ℃ / min and held for 4 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based composite hard carbon material.
[0075] Comparative Example 6 A lignin-based hard carbon material is prepared as follows (compared to Example 1, the urea-alkali dissolution system is replaced with a soda ash system). (1) Prepare a 1000 mL lignin solution with a concentration of 10 g / L by mixing 10 g of purified pine alkali lignin and 4 g of sodium hydroxide. Control the pH of the solution to 11. Add 1000 mL of cetyltrimethylammonium chloride with a concentration of 5 g / L. After reacting at 90 °C for 3 h, concentrate the solution at 90 °C until the mass fraction of the concentrate is 40 wt% to obtain a positively charged lignin solution.
[0076] (2) 500 g of a 2 wt% mechanically prepared nanocellulose dispersion (nanocellulose with a diameter of 10~30 nm and a length of 1~20 μm) was added to the above positively charged lignin solution. After stirring at 1000 rpm for 1 h, the mixture was transferred to a hydrothermal reactor and placed in a forced-air oven at 160 ℃ for 8 h. After cooling to room temperature, the reaction solution was filtered until the filtrate was neutral. The obtained solid was freeze-dried and then ground to obtain the lignin-nanocellulose composite precursor.
[0077] (3) The composite precursor was placed in a flat vulcanizing machine with a pressure of 0.2 MPa and a temperature of 180 °C. After pre-oxidation for 2 h, the cross-linked lignin-nanocellulose composite precursor was obtained.
[0078] (4) The cross-linked lignin-nanocellulose composite precursor obtained above was placed in a high-temperature tube furnace and carbonized at high temperature under the protection of argon atmosphere. The carbonization temperature was increased from room temperature to 1000 ℃ at a rate of 5 ℃ / min, and then increased to 1300 ℃ at a rate of 2.5 ℃ / min and held for 4 h. After naturally cooling to room temperature, the carbonized product was placed in a high-speed swing array ball mill and ball-milled for 3 min to obtain lignin-based composite hard carbon material.
[0079] Experimental Example The hard carbon materials obtained in Examples 1-6 and Comparative Examples 1-6 were structurally characterized, and their performance in sodium-ion battery anode materials was tested. The results are shown in Table 1 and 2. Figures 1-5 .
[0080] (1) The microstructure of the sample was characterized by scanning electron microscopy and transmission electron microscopy.
[0081] (2) The length of carbon crystals and the spacing between carbon layers in the sample were tested using an X-ray diffractometer.
[0082] (3) In the performance test of sodium-ion batteries, the lignin-based hard carbon material obtained in this invention was used to prepare the negative electrode of a sodium-ion battery with a mass ratio of 8:1:1 with polyacrylonitrile copolymer binder and conductive carbon black. A coin cell was assembled with copper sheet as positive electrode and 1 M NaPF6 as electrolyte for electrochemical testing. The test window was 0~2.5 V, and the charge / discharge current density was 0.05~5 A / g.
[0083] Table 1. Structural properties and sodium storage performance of hard carbon materials prepared in different embodiments and comparative examples.
[0084] The test results in Table 1 show that the carbon crystallite size La of the lignin-based hard carbon materials prepared in Examples 1-6 is less than 4.0 nm, Lc is about 1.0 nm, and the carbon interlayer spacing is greater than 0.385 nm. The carbon crystallite size La of Example 1 is only 3.35 nm, Lc is 1.00 nm, and the carbon interlayer spacing is 0.389 nm. Its carbon crystallite size is much smaller than that of the lignin-based hard carbon material obtained by not modifying lignin with positive charge in Comparative Example 1, the lignin-based hard carbon material obtained by not combining lignin with nanocellulose in Comparative Example 2, the lignin-based hard carbon material obtained by not hydrothermally treating the lignin solution and nanocellulose dispersion in Comparative Example 3, the lignin-based hard carbon material obtained by not pre-oxidizing the lignin-nanocellulose composite precursor in Comparative Example 4, the lignin-based hard carbon material obtained by hot pressing the nanocellulose dispersion with micron-sized cellulose powder in Comparative Example 5, and the lignin-based hard carbon material obtained by replacing the urea-alkali solution system with a soda ash system in Comparative Example 6.
[0085] In terms of electrochemical performance, the initial reversible specific capacities of Examples 1-6 were approximately the same, all around 350 mAh / g (0.05 A / g), and the specific capacities at a high current of 5 A / g were all greater than 180 mAh / g, with retention rates all exceeding 55%. The hard carbon material prepared in Example 1, as a sodium-ion anode material, exhibited an initial reversible specific capacity of 359 mAh / g, and maintained a capacity of 207 mAh / g at a high current of 5 A / g, with a retention rate of 57.7%. Its sodium storage capacity was significantly superior to that of all comparative examples, and it also demonstrated a significant advantage in rate performance.
[0086] Compared to Example 1, the lignin in Comparative Example 1 was not positively charged, causing both to aggregate independently and preventing interfacial crosslinking. Excessive carbon layer growth during carbonization resulted in longer carbon crystallites; the resulting lignin-based hard carbon had a larger carbon crystallite size La (4.98 nm) than that of Example 1, and the carbon layer spacing d... 002 (0.379 nm) is smaller than that of Example 1, resulting in extremely low sodium storage capacity and extremely poor rate performance.
[0087] In Comparative Example 2, lignin was not combined with nanocellulose, resulting in severe Π-Π aggregation of single lignin. Hot-pressing pre-oxidation alone could not suppress carbon layer condensation. The carbon layer spacing (0.375 nm) of the resulting lignin-based hard carbon was significantly lower than that of Example 1, and the carbon crystallite size was larger than that of Example 1, leading to lower sodium storage capacity and extremely poor rate performance.
[0088] In Comparative Example 3, the lignin solution and nanocellulose dispersion were not subjected to hydrothermal treatment, resulting in low cross-linking degree of lignin and nanocellulose, forming a one-dimensional / three-dimensional aggregated lignin-nanocellulose composite precursor. The resulting hard carbon material had a carbon interlayer spacing (0.376 nm) smaller than that in Example 1, resulting in a poor initial reversible capacity of 295 mAh g-1 and poor rate performance.
[0089] In Comparative Example 4, the lignin-nanocellulose composite precursor was not pre-oxidized, resulting in a low degree of oxygen crosslinking at the precursor interface. The resulting hard carbon material had a large carbon crystallite size La (4.93 nm) and a small carbon interlayer spacing (0.371 nm), leading to extremely poor rate performance and an initial reversible capacity far lower than that of Example 1.
[0090] In Comparative Example 5, the nanocellulose dispersion was replaced with micron-sized cellulose powder. Due to the relatively large particle size of the cellulose powder, the contact between lignin and cellulose was insufficient, failing to achieve the effect of electrostatic assembly. The precursor mainly exhibited 3D aggregation, resulting in a larger carbon crystallite size La (5.10 nm) in the obtained lignin-based hard carbon, and a larger carbon interlayer spacing d. 002 (0.373 nm) is significantly lower than that of the sample obtained in Example 1, resulting in extremely poor initial reversible capacity and rate performance.
[0091] In Comparative Example 6, the urea-alkali dissolution system was replaced with a soda ash system. Without urea, the hydrogen bonds of nanocellulose could not be opened, making it difficult for lignin and nanocellulose to assemble at the molecular level. This resulted in low crosslinking degree of the hard carbon precursor, leading to a larger carbon crystallite size La (4.71 nm) and a smaller carbon interlayer spacing than in Example 1 (0.379 nm), resulting in extremely poor initial reversible capacity and rate performance.
[0092] Figure 1 The image shows a SEM image of the lignin-nanocellulose composite precursor prepared in Example 1. It indicates that after electrostatic assembly and hot pressing, lignin and nanocellulose formed a good one-dimensional / three-dimensional cross-linked network structure, which effectively broke the hydrogen bonding between cellulose molecular chains and the π-π aggregation between lignin molecules.
[0093] Figure 2 The image shows a TEM image of the lignin-based composite hard carbon material prepared in Example 1. It can be seen that the hard carbon material has a high degree of disorder, a short carbon crystallite size, and a rich closed-pore structure. The high degree of disorder and the short carbon crystallite size help to shorten the charge transport path and improve the rate performance, while the rich closed-pore structure helps to fill sodium ions, thereby improving the sodium storage capacity of hard carbon.
[0094] Figure 3 The images show a comparison of XRD test results for the lignin-based composite hard carbon materials obtained in Example 1 and Comparative Examples 1-4. As can be seen from the 002 diffraction peak, Example 1 shows a significant red shift compared to the other comparative examples, indicating that the hard carbon prepared in Example 1 has the largest carbon interlayer spacing. The smaller half-peak width of its 100 diffraction peak indicates that it has a smaller carbon crystallite size.
[0095] Figure 4 The figures show the first charge-discharge curves of the lignin-based hard carbon materials prepared in Example 1 and Comparative Examples 1-4 as anode materials for sodium-ion batteries. It can be seen that the hard carbon prepared in Example 1 exhibits a high initial reversible capacity (359 mAh g⁻¹) at a current of 0.05 A / g. -1 The initial reversible capacity reached a maximum of 81.2%. The unmodified Comparative Example 1, without positive charge modification, had an initial reversible capacity of only 276 mAh g⁻¹. -1 The initial coulombic efficiency was 76.0%, significantly lower than that of Example 1. Furthermore, the initial reversible capacities of Comparative Examples 2-4, prepared without compounding with nanocellulose, without hydrothermal treatment, and without pre-oxidation, were also lower than those of Example 1.
[0096] Figure 5The figures show the rate performance curves of the lignin-based composite hard carbon materials prepared in Examples 1 and Comparative Examples 1-4 as anode materials for sodium-ion batteries. Electrostatic assembly combined with mechanical hot pressing can significantly improve the rate performance of hard carbon. The hard carbon obtained in Example 1 can maintain 207 mAh g⁻¹ under a high current of 5 A / g. -1 The high reversible capacity of the comparative examples 1-4 was significantly inferior to that of Example 1, indicating that the electrostatic assembly synergistic oxygen crosslinking technology proposed in this invention represents a significant improvement over conventional pre-oxidation technology.
[0097] In summary, the present invention employs an electrostatic assembly synergistic oxygen crosslinking method to prepare lignin-based composite hard carbon materials with large carbon interlayer spacing and small carbon microcrystals. As a negative electrode material for sodium-ion batteries, it exhibits significantly better performance than lignin-based hard carbon materials prepared by traditional methods.
[0098] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.
Claims
1. A method for preparing a lignin-based composite hard carbon material, characterized in that, Includes the following steps: (1) Dissolve lignin in a mixed solution of urea and alkali to prepare a lignin solution with a concentration of 2~10 g / L, control the pH of the solution to 10~12, then add a solution containing a positively charged reagent with a concentration of 2~10 g / L, react at 80~100 ℃ for 2~6 h, and concentrate to obtain a positively charged lignin solution. (2) The nanocellulose dispersion was added to the positively charged lignin solution and hydrothermally treated at 120~180 ℃ for 6~12 h. The resulting reaction solution was filtered and dried to obtain the lignin-nanocellulose composite precursor. (3) The lignin-nanocellulose composite precursor is pre-oxidized to obtain a highly cross-linked lignin-nanocellulose composite precursor; (4) The highly cross-linked lignin-nanocellulose composite precursor is carbonized in an inert gas to obtain the lignin-based composite hard carbon material.
2. The method for preparing lignin-based composite hard carbon material according to claim 1, characterized in that: The lignin is at least one of the following: pine alkali lignin, reed alkali lignin, bamboo alkali lignin, wheat straw alkali lignin, and corn cob alkali lignin; the alkali is at least one of the following: sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate; and the positively charged reagent is at least one of the following: hexadecyltrimethylammonium chloride, alkyldimethylbenzylammonium chloride, dicedyldimethylammonium chloride, and methyltributylammonium chloride.
3. The method for preparing lignin-based composite hard carbon material according to claim 1, characterized in that: The mass ratio of lignin:urea:alkali:positively charged reagent:nanocellulose is 100:10~50:20~100:20~100:20~200.
4. The method for preparing lignin-based composite hard carbon material according to claim 3, characterized in that: The mass ratio of lignin:urea:alkali:positively charged reagent:nanocellulose is 100:10~30:20~60:30~80:50~120.
5. The method for preparing lignin-based composite hard carbon material according to claim 1, characterized in that: The concentration is a heating concentration, with a heating temperature of 80~100 ℃, and the concentration of the positively charged lignin solution obtained is 30~50 wt%.
6. The method for preparing lignin-based composite hard carbon material according to claim 1, characterized in that: The concentration of the nanocellulose dispersion is 2-6 wt%; the nanocellulose is at least one of the following: nanocellulose prepared by mechanical method, carboxyl nanocellulose prepared by Tempo oxidation method, carboxylated nanocellulose prepared by etherification method, and carboxyl nanocellulose nanocrystals prepared by acid hydrolysis method, with a diameter of 10-30 nm and a length of 1-20 μm.
7. The method for preparing lignin-based composite hard carbon material according to claim 1, characterized in that: The hydrothermal treatment is carried out in a forced-air drying oven using a hydrothermal autoclave as the container, and the drying is vacuum drying, infrared drying, or freeze drying.
8. The method for preparing lignin-based composite hard carbon material according to claim 1, characterized in that: The pre-oxidation is carried out using a flat vulcanizing machine, with a pre-oxidation pressure of 0.1~1 MPa, a pre-oxidation temperature of 150~250 ℃, and a pre-oxidation time of 0.5~4 h; the carbonization temperature is 1000~1500 ℃, the carbonization time is 3~6 h, the heating rate is 2~5 ℃ / min, and the inert gas is nitrogen or argon.
9. The lignin-based composite hard carbon material prepared by the method described in any one of claims 1 to 8.
10. The application of the lignin-based composite hard carbon material according to claim 9 in sodium-ion battery anode materials.