A production process for preparing biomass-based hard carbon precursor material by hydrothermal method

Abstract

The present invention provides a production process for preparing biomass-based hard carbon precursor materials by a hydrothermal method. The following steps are included: S1, using biomass raw materials and water for batching to obtain slurry; S2, adding an auxiliary agent to the slurry, performing a hydrothermal reaction, setting the hydrothermal reaction temperature to 80-350°C, and stirring at a constant temperature for 1-24 hours to obtain a slurry after the reaction, wherein the auxiliary agent is a mixture of methacrylate, acrylonitrile and pyromellitic anhydride in a mass ratio of 1:0-4.5:0.05-2.5; S3, the slurry is separated into a liquid phase and a solid phase, wherein the solid phase is a crude product, the liquid phase is a mother liquor, and the crude product enters the next process; S4, washing, drying and crushing the crude product to form a carbon hard precursor material. The biomass-based hard carbon precursor material produced by the invention has an adjustable particle size, a narrow particle size distribution range, good uniformity, and low ash content.

Description

Technical Field

[0001] The invention relates to a production process for preparing a biomass-based hard carbon precursor material by a hydrothermal method, and belongs to the field of new energy and materials. Background Art

[0002] With the development of society, people's demand for electrochemical energy storage devices, especially lithium-ion batteries, has increased dramatically. However, the global distribution of lithium resources is uneven, and the metal minerals required for lithium battery manufacturing are relatively scarce, so there is an urgent need to develop new energy storage systems as a supplement to lithium batteries. Sodium-ion batteries have become a supplement to lithium-ion batteries due to their abundant resources and low cost, and have developed rapidly in recent years.

[0003] Hard carbon materials are the best commercially available negative electrode materials for sodium-ion batteries. Currently, they are mainly prepared from resin, asphalt, coal and biomass. Among them, biomass raw materials are widely available, low-cost and have relatively high capacity, and are a type of hard carbon raw materials with good commercial prospects. The particle size and ash content of hard carbon materials directly affect the electrochemical properties of hard carbon, such as the first-week coulomb efficiency, rate performance and cycle stability. Therefore, sodium-ion batteries for different purposes need to use hard carbon materials with different properties.

[0004] The existing technology for preparing hard carbon from biomass is mainly based on high-temperature pyrolysis. After high-temperature pyrolysis into carbon, acid washing is used to remove metal impurities in the raw materials and reduce the ash content of the carbon material. Although this direct pyrolysis method is simple to operate, sugar substances such as glucose and starch are prone to melting or gelatinization during the sintering process, resulting in serious agglomeration, which affects the carbonization effect and product consistency, and cannot control the particle size of the product. The acid can only contact the surface of the carbon particles, and it is difficult to remove the metal salt impurities wrapped inside the carbon particles, resulting in the final output of hard carbon ash content is too high. Moreover, during the direct pyrolysis process, a large amount of carbon elements in the biomass are converted into small molecular gaseous substances (such as carbon dioxide, carbon monoxide, etc.) and lost, resulting in low biomass utilization.

[0005] The hydrothermal method for producing biomass carbon is mostly used for the preparation of gram-level products in the laboratory. Macromolecular biomass can depolymerize at a certain temperature and pressure to form soluble small molecules. The small molecules are further aromatized and cross-linked to form materials with a high carbon content. However, the surface energy of the particles of the traditional hydrothermal product is large during the nucleation-growth process, and the particle size is difficult to control. Public patent CN 114105120 A invented a method for controlling the particle size of carbon balls at 50-200nm. This method has a narrow range of adjustment for particle size and is difficult to meet actual production needs. In addition, a large amount of carbon-containing small molecules will be produced during the hydrothermal reaction, and these substances will be dissolved in the reaction solution and discharged, resulting in a low biomass carbon yield. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a production process for preparing biomass-based hard carbon precursor materials by a hydrothermal method. The biomass-based hard carbon precursor materials produced by the hydrothermal method have adjustable particle size, narrow particle size distribution range, good uniformity and low ash content.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0008] A production process for preparing a biomass-based hard carbon precursor material by a hydrothermal method comprises the following steps:

[0009] S1 uses biomass raw materials and water to prepare slurry;

[0010] Add an auxiliary agent to the S2 slurry and perform a hydrothermal reaction. The hydrothermal reaction temperature is set to 80-350° C. and the mixture is stirred at a constant temperature for 1-24 hours to obtain a slurry after the reaction. The auxiliary agent is a mixture of methacrylate, acrylonitrile and pyromellitic anhydride in a mass ratio of 1:0-4.5:0.05-2.5.

[0011] S3 slurry is separated into liquid phase and solid phase, of which the solid phase is the crude product and the liquid phase is the mother liquor. The crude product enters the next process;

[0012] S4 washes, dries and crushes the crude product to form a carbon hard precursor material.

[0013] Furthermore, the biomass raw materials used include one or more combinations of glucose, fructose, sucrose, and starch, preferably glucose. Starch can be selected from, including but not limited to, corn starch, potato starch, and sweet potato starch. The main components of these starches are basically the same, and the difference is mainly the types and contents of vitamins and metal elements therein.

[0014] Furthermore, the mass ratio of biomass raw material to water in S1 is 1:10-35.

[0015] Furthermore, the hydrothermal reaction temperature is preferably 160-280° C., and the constant temperature stirring time is 2-5 hours.

[0016] Furthermore, the amount of the additive added in step S2 is 0.5-5wt% of the slurry obtained in step S1.

[0017] Furthermore, when the mass ratio of methacrylate, acrylonitrile and pyromellitic anhydride is 1:0-1.5:0.05-1.5, a nano-scale hard carbon precursor is synthesized; when the mass ratio of methacrylate, acrylonitrile and pyromellitic anhydride is 1:1.5-4.5:1.5-2.5, a micron-scale hard carbon precursor is synthesized.

[0018] Furthermore, the slurry is separated by centrifugation. The specific steps are: the slurry is introduced into a centrifuge, and the solid phase and the liquid phase are separated after high-speed centrifugation. The solid phase is the crude product, and the liquid phase is the mother liquor.

[0019] Furthermore, the treatment method of the mother liquor includes one or a combination of ultrafiltration, nanofiltration and reverse osmosis. The specific steps are: after the mother liquor is treated by ultrafiltration, nanofiltration or reverse osmosis, the retained organic matter is returned to the reactor for reuse, and the waste liquid is discharged after alkali neutralization treatment.

[0020] Further, the crude product is washed with water and ethanol to remove the mother liquid remaining on the surface, thereby forming a hard carbon precursor product. The drying and crushing methods of the product include hot air drying, vacuum drying, freeze drying, fluidized bed drying, grinding and crushing, air flow crushing and ultrasonic crushing, or a combination of several of them.

[0021] Furthermore, the present invention also provides a method for preparing a hard carbon material, wherein the obtained hard carbon precursor material is subjected to high temperature treatment in an inert atmosphere such as nitrogen or argon to form a hard carbon material.

[0022] Furthermore, the high temperature treatment is firstly a low temperature pre-carbonization at 400-750°C, and then a high temperature treatment at 1000-1300°C to form a hard carbon material.

[0023] The present invention further provides a hard carbon material obtained by the above preparation method.

[0024] Furthermore, the present invention provides an application of a hard carbon material as a negative electrode material for a sodium ion battery. Specifically, the hard carbon material can be mixed with a conductive agent and a binder and placed on a current collector to form a negative electrode for a sodium ion battery.

[0025] The technical solution of the present invention has the following advantages over the prior art:

[0026] The present invention prepares hard carbon precursor materials through a hydrothermal process. Biomass macromolecules are depolymerized under hydrothermal conditions, and carboxyl groups are separated from the main chain to form small molecule acids. In this process, metal ions present in the raw materials are exposed from the structure, and are combined with small molecule acids to dissolve in the mother liquor, achieving a thorough deashing effect. After the hydrothermal reaction, low ash content can still be achieved without acid washing, eliminating the acid washing process, and carbonization and deashing and impurity removal are integrated into one step, all completed in the reactor, and the process is simple and environmentally friendly.

[0027] In the hydrothermal method of the present invention, a mixture of methacrylate, acrylonitrile and pyromellitic anhydride in a mass ratio of 1:0-4.5:0.05-2.5 is added as an auxiliary agent to prepare a biomass hard carbon precursor. The process steps are simple. The particle size of the biomass-based hard carbon precursor can be regulated by adjusting the ratio of the three auxiliary agents, and the preparation of hard carbon precursor materials from nanometer to micrometer can be achieved. The particle size range of the prepared hard carbon precursor can be adjusted to be wide (50nm-10μm). This method can produce products of different particle sizes without cleaning the reaction container, which is convenient for large-scale production. Among them: methacrylate in the auxiliary agent formula of the present invention undergoes polymerization after adsorption on the particle surface, which can effectively inhibit particle growth; acrylonitrile undergoes polymerization reaction at a relatively low temperature to form microspheres, and small carbon source molecules are adsorbed on the surface to provide "seeds" for the growth of carbon spheres. Pyromellitic anhydride can undergo an esterification reaction with the hydroxyl groups on the biomass macromolecular chains, causing the molecular chains to cross-link with each other, reducing the degree of graphitization of the product after pyrolysis, and improving the quality of the hard carbon. Based on the synergistic effect of the various auxiliary components, the product particle size is adjustable and uniform, and the final hard carbon product is of high quality.

[0028] The present invention ensures high yield through the dual means of cross-linking treatment and recovery of organic matter in the mother liquor. On the one hand, after the biomass macromolecules are cross-linked by pyromellitic anhydride, the amount of small molecules produced in the hydrothermal process can be effectively reduced, the loss of carbon elements can be reduced, and the effective utilization rate of biomass macromolecules can be improved. On the other hand, the mother liquor is treated to recover small molecular organic matter and oligomers therein, and these substances are put into the reactor for reuse to continue aromatization and polymerization into carbon, so as to make full use of the carbon element in the biomass, further improve the raw material utilization rate and carbon yield rate, and reduce costs.

[0029] The process route provided by the present invention is compatible with various cheap biomass raw materials such as glucose, fructose, sucrose, starch, etc., and has high market promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to make the content of the present invention easier to understand, the present invention is further described in detail below, wherein:

[0031] Figure 1 Flow chart of the process of the present invention

[0032] Figure 2 Scanning electron microscope image of product A

[0033] Figure 3 Scanning electron microscope image of product B

[0034] Figure 4 Scanning electron microscope image of product C

[0035] Figure 5 Transmission electron microscope image of product D

[0036] Figure 6 Scanning electron microscope image of product E

[0037] Figure 7 X-ray diffraction pattern of hard carbon material HC

[0038] Figure 8 This is the first-cycle charge and discharge curve of the hard carbon material HC. DETAILED DESCRIPTION

[0039] The present invention will be further described below by means of specific embodiments:

[0040] Example 1

[0041] In this example, industrial glucose is used as a raw material to prepare a biomass hard carbon precursor, and the specific steps are as follows:

[0042] Glucose and water were added to a stirring kettle at a mass ratio of 1:30, and stirred at room temperature for 20 minutes until the slurry was evenly dispersed. 2.5wt% (based on the mass of the slurry as 100%) of sodium methacrylate-acrylonitrile-isophthalic anhydride auxiliary was added to the reactor, and the mass ratio of the three was 1:2.5:2. The slurry was heated to 250 degrees and subjected to hydrothermal reaction for 3.5 hours. After the reaction, the slurry was placed in a centrifuge and centrifuged at 1500r / min. The solid phase is the crude product and the liquid phase is the mother liquor. After ultrafiltration of the mother liquor, the organic matter is returned to the reactor for secondary production, and the waste liquid is discharged after neutralization. The solid phase crude product obtained is combined with the aforementioned crude product. The crude product is washed with water and ethanol, and after hot air drying and ball mill crushing, the hard carbon precursor powder product is obtained, which is recorded as product A. Its scanning electron microscopy shows Figure 2 ,Depend on Figure 2 It can be seen that 70% of the product is spherical particles of about 10μm (attached Figure 2 ), the average yield of three preparations was 84% ​​(yield = total carbon content in the output product / total carbon content in the raw material*100%, the same below), the carbon content of the product was determined by an element analyzer to be 70±3%, and the ash content was about 0.15% according to the national standard GB / T 3521-2008.

[0043] Example 2

[0044] The method is basically the same as Example 1, except that the hydrothermal reaction conditions are different. In this example, the hydrothermal reaction temperature is 280 degrees and the temperature is kept for 3.5 hours.

[0045] After analysis and calculation: the average yield of three preparations is 71%. After testing: the carbon content of the product is 70±3% determined by an element analyzer, and the ash content is about 0.15% according to the national standard GB / T 3521-2008.

[0046] Example 3

[0047] The method is basically the same as Example 1, except that the hydrothermal reaction conditions are different. In this embodiment, the hydrothermal reaction temperature is 160 degrees and the temperature is kept for 3.5 hours. According to the national standard GB / T 3521-2008, the ash content is about 0.15%.

[0048] Example 4

[0049] In this example, industrial glucose is used as a raw material to prepare a biomass hard carbon precursor, and the specific steps are as follows:

[0050] It is basically the same as Example 1, except that the hydrothermal reaction conditions are different. In this embodiment, the hydrothermal reaction temperature is 250 degrees and the temperature is kept for 3.5 hours; only the solid phase product is collected, and the mother liquor is not reused. The collected solid phase product is washed with water and ethanol to obtain a crude product, which is then dried with hot air and crushed with a ball mill to obtain a hard carbon precursor powder product. After analysis and calculation: the average yield of three preparations is 78%. The carbon content of the product is determined to be 70±3% using an elemental analyzer, and the ash content is about 0.15% according to the national standard GB / T 3521-2008.

[0051] Example 5

[0052] In this example, industrial glucose is used as a raw material to prepare a biomass hard carbon precursor, and the specific steps are as follows:

[0053] Add glucose and water in a mass ratio of 1:10 into a stirring kettle, and stir at room temperature for 20 minutes until the slurry is evenly dispersed. Add 3wt% (based on 100% mass of the slurry) of sodium methacrylate-acrylonitrile-pyromellitic anhydride additives to the reactor, and the mass ratio of the three is 1:0:0.5. Heat the slurry to 250 degrees and keep it warm for 3.5 hours. After the reaction is completed, place the slurry in a centrifuge and centrifuge it at 1500r / min. The solid phase is the crude product and the liquid phase is the mother liquor. After ultrafiltration of the mother liquor, the organic matter is returned to the reactor for subsequent production, and the waste liquid is discharged after neutralization. The crude product is washed with water and ethanol, and after hot air drying and ball mill crushing, the hard carbon precursor powder product is obtained, which is recorded as product B. Its scanning electron microscopy shows Figure 3 ,Depend on Figure 3 It can be seen that the product is a spherical particle of about 50nm (attached Figure 3 ), the particle size distribution range is: 40-65nm. The carbon content of the product is 70±3% measured by an element analyzer, and the ash content is about 0.15% according to the national standard GB / T 3521-2008.

[0054] Example 6

[0055] In this example, industrial glucose is used as a raw material to prepare a biomass hard carbon precursor, and the specific steps are as follows:

[0056] Add glucose and water in a mass ratio of 1:30 into a stirring kettle, and stir at room temperature for 20 minutes until the slurry is evenly dispersed. Add 2.5wt% (based on 100% mass of the slurry) of sodium methacrylate-acrylonitrile-pyromellitic anhydride auxiliary to the reactor, and the mass ratio of the three is 1:1.5:1.5. Heat the slurry to 250 degrees and keep it warm for 3.5 hours. After the reaction is completed, place the slurry in a centrifuge and centrifuge it at 1500r / min. The solid phase is the crude product and the liquid phase is the mother liquor. After ultrafiltration of the mother liquor, the organic matter is returned to the reactor for subsequent production, and the waste liquid is discharged after neutralization. The crude product is washed with water and ethanol, and after hot air drying and ball mill crushing, the hard carbon precursor powder product is obtained, which is recorded as product C. Its scanning electron microscopy shows Figure 4 ,Depend on Figure 4 It can be seen that the product is a spherical particle of about 2μm (attached Figure 4 ), the particle size distribution range is: 1.5-2.5μm. The carbon content of the product is 70±3% measured by an element analyzer, and the ash content is about 0.15% according to the national standard GB / T 3521-2008.

[0057] Example 7

[0058] In this example, industrial glucose is used as a raw material to prepare a biomass hard carbon precursor, and the specific steps are as follows:

[0059] Glucose and water are added to a stirring kettle at a mass ratio of 1:30, and stirred at room temperature for 20 minutes until the slurry is evenly dispersed. Add 2.5wt% (based on 100% mass of the slurry) of sodium methacrylate-acrylonitrile-pyromellitic anhydride auxiliary to the reactor, and the mass ratio of the three is 1:1.1:0.8. Heat the slurry to 250 degrees and keep it warm for 3.5 hours. After the reaction is completed, place the slurry in a centrifuge and centrifuge it at 1500r / min. The solid phase is the crude product and the liquid phase is the mother liquor. After ultrafiltration of the mother liquor, the organic matter is returned to the reactor for subsequent production, and the waste liquid is discharged after neutralization. The crude product is washed with water and ethanol, and after hot air drying and ball mill crushing, the hard carbon precursor powder product is obtained, which is recorded as product D. Its scanning electron microscopy shows Figure 5 ,Depend on Figure 5 It can be seen that the product is a spherical particle of about 100nm (attached Figure 5 ), the particle size distribution range is: 70-110nm. The carbon content of the product is 70±3% measured by an element analyzer, and the ash content is about 0.15% according to the national standard GB / T 3521-2008.

[0060] Example 8

[0061] In this embodiment, corn starch is used as a raw material to prepare a biomass hard carbon precursor, and the specific steps are as follows:

[0062] Corn starch and water are added to a stirring kettle at a mass ratio of 1:35, and stirred at room temperature for 20 minutes until the slurry is evenly dispersed. Add 2.5wt% (based on 100% mass of the slurry) of sodium methacrylate-acrylonitrile-pyromellitic anhydride additives to the reactor, and the mass ratio of the three is 1:1.8:2.3. Heat the slurry to 250 degrees and keep it warm for 3.5 hours. After the reaction is completed, place the slurry in a centrifuge and centrifuge it at 1500r / min. The solid phase is the crude product and the liquid phase is the mother liquor. After ultrafiltration of the mother liquor, the organic matter is returned to the reactor for subsequent production, and the waste liquid is discharged after neutralization. The crude product is washed with water and ethanol, and after hot air drying and ball mill crushing, the hard carbon precursor powder product is obtained, which is recorded as product E. Its scanning electron microscopy shows Figure 6 ,Depend on Figure 6 It can be seen that the product is spherical particles of about 0.7 μm (attached Figure 6 ), the particle size distribution range is: 0.5-1.0μm. According to the national standard GB / T 3521-2008 test, the product ash content is 0.2%.

[0063] Example 9

[0064] The biomass precursor of the present invention can be carbonized to obtain hard carbon material for sodium ion batteries, and the specific steps are as follows:

[0065] Product A was heated to 600°C at a rate of 5°C / min in a nitrogen atmosphere, kept at this temperature for 2 hours, then heated to 1100°C at a rate of 2°C / min, kept at this temperature for 2 hours, and then cooled naturally to obtain hard carbon material HC. The X-ray diffraction spectrum test showed that the HC sample had no obvious diffraction peaks and exhibited typical hard carbon characteristics (see attached). Figure 7 HC, conductive carbon black and binder were coated on aluminum foil in a ratio of 8:1:1 to form a pole piece. The half-cell test showed that the reversible specific capacity of the HC material was 305 mAh / g and the first-week coulomb efficiency was 91.4% (see Appendix Figure 8 ), can be used as a negative electrode material for sodium-ion batteries with excellent performance.

[0066] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and scope of the equivalent elements of the claims are included in the present invention.

[0067] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A production process for preparing biomass-based hard carbon precursor materials by a hydrothermal method, characterized in that: The following steps are involved: S1 uses biomass raw materials and water to prepare slurry, the mass ratio of biomass raw materials to water in S1 is 1:10-35, and the amount of additives added in step S2 is 0.5-5wt% of the slurry obtained in S1; Add an auxiliary agent to the S2 slurry and perform a hydrothermal reaction. The hydrothermal reaction temperature is set to 80-350° C. and the mixture is stirred at a constant temperature for 1-24 hours to obtain a slurry after the reaction. The auxiliary agent is a mixture of methacrylate, acrylonitrile and pyromellitic anhydride in a mass ratio of 1:0-4.5:0.05-2.

5. S3 slurry is separated into liquid phase and solid phase, of which the solid phase is the crude product and the liquid phase is the mother liquor. The crude product enters the next process; S4 washes, dries and crushes the crude product to form a carbon hard precursor material. The mass ratio of methacrylate, acrylonitrile and pyromellitic anhydride in S2 is 1:0-1.5:0.05-1.5, and a nano-scale hard carbon precursor is synthesized; when the mass ratio of methacrylate, acrylonitrile and pyromellitic anhydride is 1:1.5-4.5:1.5-2.5, a micron-scale hard carbon precursor is synthesized.

2. The production process according to claim 1, characterized in that: The biomass raw materials used include one or a combination of glucose, fructose, sucrose and starch.

3. The production process according to claim 1, characterized in that: The hydrothermal reaction temperature is 160-280°C, and the constant temperature stirring time is 2-5 hours.

4. The production process according to claim 1, characterized in that: The slurry is separated by centrifugation. The slurry is introduced into a centrifuge and separated into a solid phase and a liquid phase after high-speed centrifugation. The solid phase is a crude product and the liquid phase is a mother liquor. The treatment methods for the mother liquor include one or a combination of ultrafiltration, nanofiltration and reverse osmosis. After the mother liquor is treated with ultrafiltration, nanofiltration or reverse osmosis, the retained organic matter is returned to the reactor for reuse, and the waste liquid is discharged after alkali neutralization treatment.

5. A method for preparing a hard carbon material, characterized in that: The hard carbon precursor material produced according to any one of claims 1 to 4 is subjected to high temperature treatment under an inert atmosphere to form a hard carbon material.

6. The preparation method according to claim 5, characterized in that: The high temperature treatment is to first pre-carbonize at a low temperature of 400-750°C, and then heat up to a high temperature of 1000-1300°C to form a hard carbon material.

7. The hard carbon material prepared according to the preparation method of claim 5 or 6.

8. Use of the hard carbon material according to claim 7 as a negative electrode material for a sodium ion battery.

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