Preparation method of modified biomass hard carbon material

Abstract

The application relates to a preparation method of a modified biomass hard carbon material, which comprises the following steps: after a treated biomass charcoal is subjected to an epoxidation and a modification treatment of tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate, the treated biomass charcoal is subjected to gradient calcination. The application uses cheap and readily available biomass as a carbon source, performs modification after carbonization, and finally performs staged and stepped calcination, so that the biomass hard carbon material with excellent electrochemical performance is obtained, and the application provides a modification direction of the hard carbon material for industrialization of sodium ion batteries.

Description

Technical Field

[0001] This invention belongs to the technical field of hard carbon materials for sodium-ion batteries, specifically relating to a method for preparing modified biomass hard carbon materials. Background Technology

[0002] Lithium-ion batteries are widely used, but due to the limited availability of lithium resources, the price of lithium sources has been rising year by year. While sodium-ion batteries have a lower capacity than lithium-ion batteries, they are still a promising battery material for industrialization. Currently, the electrochemical performance of sodium-ion battery anode materials does not yet meet the needs of practical industry. + The large radius and atomic mass of sodium ions result in poor insertion / extraction kinetics, making it difficult for them to intercalate into anode materials. This leads to poor electrochemical performance of conventional silicon-based anode materials in sodium-ion batteries, affecting aspects such as capacity, initial efficiency, rate performance, and cycle stability. Hard carbon materials are a hot research area in sodium-ion battery research.

[0003] Biomass-derived hard carbon materials are a promising candidate for large-scale industrial production of sodium-ion battery anode materials due to their readily available and inexpensive raw materials. However, current performance characteristics of biomass hard carbon materials include low capacity, low initial efficiency, and low energy density. Consequently, biomass hard carbon materials are currently largely in the research stage and have not yet seen large-scale practical applications.

[0004] CN1165553518A discloses a method for preparing hard carbon anode materials. The method involves crushing biomass materials such as cottonseed, walnut shells, and apricot shells, carbonizing them at 1000-1200℃, acid washing to remove impurities, drying, and adding crosslinking agents, dispersants, and pore-forming agents to form nanopores on the carbon source surface. This modified hard carbon material improves sodium ion transport channels, obtains more sodium storage sites, and enhances the electrochemical performance of the hard carbon material. However, this patented process is complex, and the addition of pore-forming agents, if not properly controlled, can result in excessive porosity in the hard carbon material, which is detrimental to the electrochemical performance of the anode.

[0005] CN115259150A discloses a biomass hard carbon material, which is prepared by ultrasonically cleaning, crushing, carbonizing, and activating pine cones to obtain activated carbonized components and then preparing doped carbonized components together with dopants, followed by high-temperature sintering to obtain biomass hard carbon material. However, the preparation process of the dopants is too complex, requiring multiple synthesis steps, and is not suitable for industrial production.

[0006] CN114388736A discloses a method for preparing hard carbon anodes for sodium-ion batteries using biomass carbon. The method involves modifying biomass carbon through acid washing, ball milling, and carbonization to obtain the hard carbon anode material. The modification involves impregnating the biomass carbon in a solution of DMF and m-aminophenylurea hydrochloride at a volume ratio of 1-5:3. The hard carbon material has fewer surface defects and improved electrochemical performance.

[0007] CN11323440A discloses a hard carbon anode material with high initial efficiency and excellent cycle life. However, carbon nanotubes are added to the raw materials to increase the conductivity of the material. Carbon nanotubes are expensive, and even a small amount added will increase the production cost of hard carbon materials, deviating from the original intention of using inexpensive and readily available biomass carbon sources.

[0008] Furthermore, hard carbon materials have large interlayer spacing, resulting in a larger specific capacity. However, due to the complex pore structure, sodium cannot be inserted / extracted, leading to low first-cycle coulombic efficiency and a reversible capacity lower than the theoretical capacity.

[0009] Therefore, there is an urgent need to develop a method for preparing hard carbon anode materials for sodium-ion batteries that uses biomass materials, is low in cost, and is suitable for industrial production. Summary of the Invention

[0010] To address the shortcomings of existing hard carbon anode materials, such as high manufacturing costs and poor electrochemical performance, this invention proposes a method for preparing modified biomass hard carbon materials.

[0011] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0012] A method for preparing modified biomass hard carbon material includes the following steps:

[0013] (S1) The biomass is successively crushed, soaked in hot alkaline aqueous solution, and washed with water;

[0014] (S2) The biomass obtained in step (S1) is fed into a rotary atmosphere furnace for carbonization;

[0015] (S3) The carbonized material is subjected to flotation, hydrochloric acid washing, water washing, and grinding to obtain carbonized particles;

[0016] (S4) The carbonized particles are successively subjected to epoxidation, impregnation with tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate solution, water washing, and alcohol washing to obtain modified carbonized particles;

[0017] (S5) The modified carbonized particles are calcined in a graphite furnace, followed by secondary hydrochloric acid rinsing, water washing, drying, and grading to obtain a modified biomass hard carbon material.

[0018] Furthermore, in step (S1), the biomass is selected from at least one of coconut shells, palm shells, bamboo blocks, walnut shells, and apricot shells. This invention utilizes readily available raw materials, ensuring the needs of large-scale industrial production.

[0019] Further, in step (S1), the crushing is to crush to 80-325 mesh. The crushing method is not particularly limited, as long as the crushed material reaches the specified mesh size; for example, air jet crushing, high-speed crushing, ball milling, etc., are acceptable. The hot alkaline aqueous solution impregnation involves impregnation in a 50-60℃, 5-10wt% NaOH and / or KOH aqueous solution under stirring at 60-100 rpm for 2-4 hours. The washing process continues until the effluent is neutral (pH = 7-7.5).

[0020] Further, in step (S2), the carbonization is carried out in a rotary kiln at a rotation speed of 0.5-2 rpm and a carbonization temperature of 400-600℃ for 4-8 hours, and the volatile matter content of the carbonized material is ≤5%.

[0021] Further, in step (S3), the flotation is a flow-through bubbling flotation method to separate the light and heavy components of the carbonized material. With the electromagnetic device installed in the flotation cell, iron impurities and ash components such as mud and sand can be initially removed, reducing the ash content and iron content of the carbonized material. The hydrochloric acid rinsing involves mixing and stirring the flotated carbonized material with a dilute hydrochloric acid solution in a reactor, then treating it under reflux conditions for 2-4 hours. The concentration of the dilute hydrochloric acid is 3-8 wt%, and the amount of dilute hydrochloric acid used is 4-6 times the mass of the flotated carbonized material. The purpose of rinsing is to remove metallic ash impurities. The water washing is performed until the effluent is neutral (pH = 6.8-7). The grinding is performed until the material's D50 is 5-10 μm. The grinding equipment is not particularly limited; conventional equipment in the field is acceptable, such as an air jet mill.

[0022] Further, in step (S4), the epoxidation involves feeding the carbonized particles into a 3-5 wt% NaOH and / or KOH solution at 5-10 times their mass, heating to 50-60°C, and slowly adding 0.3-0.4 times their mass of epichlorohydrin under an inert atmosphere. The reaction is maintained at this temperature for 4-6 hours. Then, 0.1-0.15 times their mass of solid NaOH and / or KOH are added, and the reaction is maintained at this temperature for another 2-4 hours. The solvent and unreacted epichlorohydrin are removed by vacuum distillation, and the mixture is dried to obtain epoxidized carbonized particles. The tris[2-(3-mercaptopropionic acid)ethyl] The isocyanurate solution impregnation method involves impregnating the obtained epoxidized carbonized particles in a solution of 10-15 times their mass of tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate, adding an organic amine, and reacting at 50-60°C for 4-6 hours. The solvent in the solution is at least one of tetrahydrofuran and dioxane. The mass concentration of tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate is 10-15 wt%, and the amount of organic amine added is 10-20% of the mass of tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate, wherein the organic amine is selected from at least one of triethylamine and trimethylamine. The reactivity of the epoxy and mercapto groups is slightly insufficient; adding a small amount of organic amine as a catalyst can significantly improve the reaction efficiency.

[0023] This invention creatively modifies biomass carbon sources, epoxidizes them, and then reacts them with tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate under organic amine catalysis to form a certain cross-linked structure. This reduces defects in the sintered hard carbon material, improves its microstructure, and is more conducive to enhancing the electrochemical performance of the hard carbon material. Tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate simultaneously serves the purposes of cross-linking modification and doping modification. Heteroatom doping has been proven to be an effective means of improving the electrochemical performance of hard carbon anode materials. Introducing nitrogen doping is the most studied doping method, which can improve the activity and electronic conductivity of hard carbon materials. Some studies have used nitrogen sources such as urea and melamine to calcine with biomass carbon sources to obtain nitrogen-doped hard carbon materials. The inventors unexpectedly discovered that modifying biomass carbon sources with tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate, along with N and S doping and crosslinking modification, synergistically improved the electrochemical properties of hard carbon materials. Its reversible specific capacity, first-efficiency performance, cycle stability, and rate performance were all enhanced simultaneously. Sulfur atoms, with their relatively large size, increase interlayer spacing in hard carbon materials, facilitating sodium ion insertion / extraction; moreover, sulfur atoms themselves possess electrochemical activity, increasing sodium storage capacity. The inventors had previously experimented with other nitrogen and sulfur sources, such as melamine, urea, sulfur powder, thiophene, and sulfur-containing amino acids, but even with the same N and S doping ratios, the electrochemical performance improvement of hard carbon materials obtained using tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate as the dopant source was not as significant. Although the reason is unclear, the use of [2-(3-mercaptopropoxy)ethyl]isocyanurate as a dopant source for hard carbon materials is reported for the first time, and it greatly improves the electrochemical performance of hard carbon materials.

[0024] Furthermore, in step (S5), the calcination is a staged gradient calcination. The gradient calcination process involves heating the material in a graphite furnace first to 700-800℃ at a heating rate of 5-10℃ / min and holding for 1-2 hours, then heating it to 1000-1300℃ at a heating rate of 5-10℃ / min and holding for 2-4 hours, followed by cooling to 300-500℃ and holding for 1-2 hours, and finally cooling to room temperature. This gradient calcination process is beneficial for adjusting the microstructure of the carbonized material, resulting in hard carbon materials with suitable interlayer spacing.

[0025] Further, in step (S5), the secondary rinsing is the same as the aforementioned rinsing steps and conditions. Specifically, in the reactor, the dilute hydrochloric acid solution and the carbonized material after gradient calcination are mixed and stirred evenly, and then treated under reflux conditions for 2-4 hours. The concentration of dilute hydrochloric acid is 3-8 wt%, and the amount of dilute hydrochloric acid used is 4-6 times the mass of the carbonized material after gradient calcination. The purpose of rinsing is to further remove metallic ash impurities and improve the quality of the hard carbon material. The drying process is to dry to a moisture content ≤1%. There are no particular limitations on the drying process, such as paddle dryer, vacuum drying, etc. The grading process is to grade the dried semi-finished product to meet the particle size requirements: D10 > 2 μm, D50 is 5-10 μm, and D90 ≤ 25 μm. After grading, the finished modified biomass hard carbon material is obtained.

[0026] The present invention also provides a sodium-ion battery, wherein the negative electrode active material comprises the modified biomass hard carbon material prepared by the above preparation method.

[0027] The present invention also provides the use of tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate as a modifier in the preparation of hard carbon anode materials.

[0028] The superior effect of this invention lies in using inexpensive and readily available biomass as a carbon source. After carbonization, the biomass is modified. First, the surface of the carbonized particles is epoxidized. Then, the epoxidized carbonized particles react with tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate to obtain modified carbonized particles. Finally, a segmented step calcination is performed to obtain biomass hard carbon materials with excellent electrochemical performance. Attached Figure Description

[0029] Figure 1 This is a photograph of the hard carbon material prepared in Example 1;

[0030] Figure 2 This is the XRD pattern of the hard carbon material prepared in Example 1;

[0031] Figure 3 This is a SEM image of the hard carbon material prepared in Example 1;

[0032] Figure 4 This is a partial enlarged SEM image of the hard carbon material prepared in Example 1. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. The following embodiments are provided to better understand this invention, but do not limit the invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods.

[0034] Example 1

[0035] (S1) The coconut shells were crushed to 200 mesh by a high-speed crusher and then immersed in a 50℃ 5wt% NaOH aqueous solution under stirring at 100rpm for 4 hours. After that, the shells were washed with water until the pH of the effluent was 7.5.

[0036] (S2) The crushed coconut shells obtained in step (S1) are fed into a rotary atmosphere furnace for carbonization. The carbonization conditions are: nitrogen atmosphere, rotary furnace rotation speed of 1 rpm, carbonization temperature of 500℃, carbonization treatment for 6 hours, to obtain coconut shell charcoal with volatile matter ≤3wt%.

[0037] (S3 coconut shell charcoal undergoes flow flotation to separate the light and heavy components of the carbonized material, and initially removes iron impurities, mud, sand and other ash components; the flotation-treated coconut shell charcoal is fed into a reactor, and 5wt% dilute hydrochloric acid at 6 times the weight of the coconut shell charcoal is added. The coconut shell charcoal is then rinsed with hydrochloric acid under reflux conditions; it is then ground to a particle size of 7±2μm using an air jet mill to obtain carbonized particles.)

[0038] (S4) The carbonized particles were fed into a 5wt% NaOH aqueous solution at 6 times their mass, heated to 50°C, and under nitrogen atmosphere with stirring, 0.3 times their mass of epichlorohydrin was slowly added. The reaction was maintained at this temperature for 4 hours. Then, 0.1 times their mass of solid NaOH was added, and the reaction was maintained at this temperature for another 2 hours. The solvent and unreacted epichlorohydrin were removed by vacuum distillation, and the particles were dried in a vacuum oven to obtain epoxidized carbonized particles. The obtained epoxidized carbonized particles were impregnated in a tetrahydrofuran solution of 10wt% of tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate at 10 times their mass of the epoxidized carbonized particles. Triethylamine at 10% of the mass of tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate was added, and the reaction was maintained at 50°C for 6 hours. The mixture was cooled to room temperature, filtered, and the obtained carbonized particles were washed with water and then with ethanol. The particles were then dried to obtain modified carbonized particles.

[0039] (S5) The obtained modified carbonized particles were subjected to gradient calcination in a graphite furnace. Specifically, the temperature was first increased to 700℃ at a heating rate of 5℃ / min and held for 1 hour; then increased to 1000℃ at a heating rate of 5℃ / min and held for 4 hours; cooled to 500℃ and held for 1 hour; and finally cooled to room temperature. The obtained carbon material was fed into a reactor, and 5wt% dilute hydrochloric acid (4 times the mass of the carbon material) was added. The mixture was heated under reflux and rinsed twice with hydrochloric acid to further remove metal ash impurities. Excess salts and other impurities were removed by water washing, and the mixture was dried in a vacuum oven until the moisture content was ≤1%. The dried semi-finished product was graded to meet the particle size requirements: D10 > 2μm, D50 5-10μm, D90 ≤ 25μm. After grading, the finished modified biomass hard carbon material was obtained.

[0040] Figure 1 This is a photograph of the hard carbon material prepared in Example 1.

[0041] Figure 2 This is the XRD pattern of the hard carbon material prepared in Example 1.

[0042] Figure 3 This is a SEM image of the hard carbon material prepared in Example 1. Figure 4 This is a partial enlarged SEM image of the hard carbon material prepared in Example 1. It can be seen that the particle size of the hard carbon material prepared in Example 1 is around 5-10 μm, and the particle size distribution is relatively uniform.

[0043] Example 2

[0044] The other conditions and operations are the same as in Example 1, except that the biomass material, coconut shell, is replaced with palm shell.

[0045] Example 3

[0046] The other conditions and operations are the same as in Example 1, except that the biomass material, coconut shells, is replaced with walnut shells.

[0047] Example 4

[0048] Other conditions and operations are the same as in Example 1. The difference is that in step (S5), instead of performing staged gradient calcination, the obtained modified carbonized particles are heated to 1000°C in a graphite furnace at a heating rate of 5°C / min and held for 6 hours, and then cooled to room temperature.

[0049] Example 5

[0050] Other conditions and operations are the same as in Example 1. The difference is that in step (S5), the gradient calcination treatment is to first heat the temperature to 800°C at a heating rate of 5°C / min and hold it for 1 hour; then heat the temperature to 1100°C at a heating rate of 5°C / min and hold it for 4 hours; cool the temperature to 500°C and hold it for 1 hour; and finally cool the temperature to room temperature.

[0051] Example 6

[0052] Other conditions and operations are the same as in Example 1. The difference is that in step (S5), the gradient calcination treatment is to first heat the temperature to 750°C at a heating rate of 5°C / min and hold it for 1 hour; then heat the temperature to 1300°C at a heating rate of 5°C / min and hold it for 4 hours; cool the temperature to 300°C and hold it for 2 hours; and finally cool the temperature to room temperature.

[0053] Comparative Example 1

[0054] The other conditions and operations are the same as in Example 1, except that step (S4) is omitted and the carbonized particles obtained in step (S3) are directly subjected to gradient calcination and other treatments in step (S5).

[0055] Example of effect

[0056] The modified biomass hard carbon materials obtained in the above examples and comparative examples were tested. Specifically, the hard carbon materials prepared in the examples or comparative examples were used as active ingredients and mixed with 1% CMC binder, Super P and SBR conductive agents at a mass ratio of 1.88:2.4:0.05:0.12. The mixture was then dispersed in a degassing machine to form a uniform negative electrode slurry. An automatic coating and drying machine was used to uniformly coat the negative electrode slurry onto an aluminum foil current collector with a scraper, achieving a coating thickness of 140±1μm. After vacuum drying, a 14mm diameter circular electrode sheet was formed. A sodium sheet was used as the counter electrode, glass fiber was used as the separator, and the electrolyte was 1M NaClO4 in EC:PC = 1:1 with 5% FEC. The half-cell was assembled in a glove box. After assembly, it was tested at 12mAh·g -1 The test was conducted at a current density of (0.1C), with a test range of 0.001-2.0V. Table 1 below shows the composition of the sodium-ion battery anode material of this invention.

[0057] Table 1. Formulation of sodium-ion battery anode materials

[0058]

[0059] The test results are shown in Table 2 below.

[0060] Table 2 Performance Tests of Hard Carbon Materials

[0061]

[0062] It can be seen that the modified biomass hard carbon material prepared by the method of this invention, as a negative electrode active material for sodium-ion batteries, exhibits excellent comprehensive electrochemical performance. Its capacity, initial efficiency, rate performance, and cycle stability are significantly improved compared to unmodified hard carbon material. This improvement is attributed to tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate as a modifier. Such a significant improvement could not be achieved with other nitrogen- and / or sulfur-containing modifiers.

Claims

1. A method for preparing a modified biomass hard carbon material, characterized in that, Includes the following steps: (S1) The biomass is successively crushed, soaked in hot alkaline aqueous solution, and washed with water; (S2) The biomass obtained in step (S1) is fed into a rotary atmosphere furnace for carbonization; (S3) The carbonized material is subjected to flotation, hydrochloric acid rinsing, water washing, and grinding to obtain carbonized particles. (S4) The carbonized particles are sequentially subjected to epoxidation, impregnation in tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate solution, washing with water, and washing with alcohol to obtain modified carbonized particles; the epoxidation is performed by feeding the carbonized particles into a solution containing 3-5 wt% of 5-10 times their mass. In a NaOH and / or KOH solution, the temperature is raised to 50-60℃, and under an inert atmosphere, 0.3-0.4 times the mass of the carbonized particles in epichlorohydrin is slowly added. The reaction is maintained at this temperature for 4-6 hours. Then, 0.1-0.15 times the mass of the carbonized particles in solid NaOH and / or KOH is added, and the reaction is maintained at this temperature for another 2-4 hours. The solvent and unreacted epichlorohydrin are removed by vacuum distillation, and the mixture is dried to obtain epoxidized carbonized particles. The impregnation with tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate solution involves impregnating the obtained epoxidized carbonized particles in a solution of 10-15 times the mass of tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate, adding an organic amine, and reacting at 50-60℃ for 4-6 hours. (S5) The modified carbonized particles are calcined in a graphite furnace, followed by secondary hydrochloric acid rinsing, water washing, drying, and grading to obtain modified biomass hard carbon material.

2. The preparation method according to claim 1, characterized in that, In step (S1), the biomass is selected from at least one of coconut shell, palm shell, bamboo block, walnut shell, and apricot shell.

3. The preparation method according to claim 1, characterized in that, In step (S1), the crushing is to crush to 80-325 mesh; the hot alkaline aqueous solution immersion is to immerse in a 50-60℃, 5-10wt% NaOH and / or KOH aqueous solution under stirring at 60-100rpm for 2-4h; and the water washing is performed until the effluent is neutral.

4. The preparation method according to claim 1, characterized in that, In step (S2), the carbonization is carried out in a rotary kiln at a rotation speed of 0.5-2 rpm and a carbonization temperature of 400-600℃ for 4-8 hours, and the volatile matter of the carbonized material is ≤5%.

5. The preparation method according to claim 1, characterized in that, In step (S3), the flotation is carried out by a flow-through flotation method; the hydrochloric acid rinsing is carried out in a reactor by mixing and stirring the dilute hydrochloric acid solution and the carbonized material after flotation, and then treating it under reflux conditions for 2-4 hours. The concentration of dilute hydrochloric acid is 3-8 wt%, and the amount of dilute hydrochloric acid used is 4-6 times the mass of the carbonized material after flotation; the water washing is carried out until the effluent is neutral; and the grinding is carried out until the material D50 is 5-10 μm.

6. The preparation method according to claim 1, characterized in that, In step (S4), the solvent for the solution of tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate is at least one of tetrahydrofuran and dioxane, the mass concentration of tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate is 10-15 wt%, and the amount of organic amine added is 10-20% of the mass of tris[2-(3-mercaptopropionic acid)ethyl]isocyanurate.

7. The preparation method according to claim 1, characterized in that, In step (S5), the calcination is a staged gradient calcination. The gradient calcination treatment is carried out in a graphite furnace. First, the temperature is raised to 700-800℃ at a heating rate of 5-10℃ / min and held for 1-2 hours. Then, the temperature is raised to 1000-1300℃ at a heating rate of 5-10℃ / min and held for 2-4 hours. Next, the temperature is cooled to 300-500℃ and held for 1-2 hours. Finally, the temperature is cooled to room temperature.

8. The preparation method according to claim 1, characterized in that, In step (S5), the secondary hydrochloric acid rinsing involves mixing and stirring a dilute hydrochloric acid solution with the carbonized material after gradient calcination in a reaction vessel, then refluxing for 2-4 hours. The concentration of the dilute hydrochloric acid is 3-8 wt%, and the amount of dilute hydrochloric acid used is 4-6 times the mass of the carbonized material after gradient calcination. The grading involves classifying the dried semi-finished product to meet the particle size requirements: D10 > 2 μm, D50 5-10 μm, and D90 ≤ 25 μm. After grading, the finished modified biomass hard carbon material is obtained.

9. A sodium-ion battery, characterized in that, The sodium-ion battery negative electrode active material includes the modified biomass hard carbon material prepared by any one of the preparation methods of claims 1-8.

Images