Method for preparing hard carbon from biomass material, hard carbon and application thereof

Abstract

The application discloses a method for preparing hard carbon from biomass material and the hard carbon and application, and belongs to the technical field of negative electrode materials of sodium ion batteries. The application provides a preparation method of hard carbon, which comprises the following steps: mixing and grinding aromatic acid and a solvent to obtain an aromatic acid suspension; adding the aromatic acid suspension into starch after heating to uniformly mix to obtain a gelatinized starch and aromatic acid mixture; performing heating reaction and pre-burning on the gelatinized starch and aromatic acid mixture in a reactor to obtain a precursor; and performing high-temperature carbonization and airflow crushing on the precursor to obtain hard carbon. The method introduces aromatic rings into starch molecules by performing reaction on gelatinized starch and aromatic acid, and a complex cross-linking structure with aromatic rings as nodes is obtained. The hard carbon prepared by performing high-temperature carbonization on the precursor after pre-burning has longer curled graphite microcrystals, forms more micropores and has a larger closed pore volume. The prepared hard carbon applied to sodium ion batteries as a negative electrode has better sodium storage performance.

Description

Technical Field

[0001] This application belongs to the field of sodium-ion battery anode material technology, and particularly relates to a method for preparing hard carbon from biomass materials, as well as the application of hard carbon. Background Technology

[0002] Electrode materials are a crucial component of batteries, directly determining their specific energy and lifespan. Currently, sodium-ion batteries have broad application prospects in low-speed electric vehicles and large-scale energy storage. However, scalable, low-cost, and high-performance sodium-ion battery anode materials still face numerous challenges. Hard carbon, as a recognized practical anode material for sodium-ion batteries, boasts advantages such as simple preparation processes, low sodium storage potential, and high capacity, making it the most widely researched anode material for sodium-ion batteries. Biomass materials are commonly used precursors for hard carbon preparation, with commonly used biomass types including straw, corn cobs, and coconut shells. Due to differences in the type, composition, and structure of biomass precursors, the performance of the prepared hard carbon anode materials is inconsistent, resulting in poor batch-to-batch stability. This limits the large-scale application of hard carbon preparation technology using biomass materials. Summary of the Invention

[0003] This application provides a method for preparing hard carbon from biomass materials and the application of hard carbon. The method involves refining aromatic acid particles, gelatinizing starch using a high-temperature solvent, and uniformly mixing the starch with the aromatic acid. Then, at a certain temperature, the active hydroxyl groups in the starch molecules cross-link with the carboxylic acid groups in the aromatic acid, forming a complex cross-linked structure with aromatic rings as nodes. Further increasing the temperature causes the material to decompose and foam, yielding a precursor. This precursor is then carbonized at high temperature to obtain hard carbon. This method utilizes the active hydroxyl groups in the starch molecule's own structure to cross-link with the aromatic acid. The cross-linking polymerization process introduces abundant C=O groups and aromatic ring structures into the precursor molecule structure, effectively preventing the formation of an ordered graphite layer crystal structure during high-temperature carbonization. The resulting hard carbon has a longer, coiled, disordered carbon layer, resulting in high specific capacity and high initial coulombic efficiency. The controlled decomposition and foaming of the material after heating to obtain the precursor, followed by the preparation of hard carbon, results in a hard carbon with a low specific surface area and abundant closed-cell structure, exhibiting high sodium storage capacity and high initial coulombic efficiency. The method also features low raw material and process costs, making it suitable for large-scale production.

[0004] This application provides the following technical solution:

[0005] In a first aspect, this application provides a method for preparing hard carbon from biomass materials, comprising the following steps:

[0006] S1, Aromatic acid is placed in a solvent and ground to obtain an aromatic acid suspension;

[0007] S2, Heat the aromatic acid suspension obtained in step S1, then add starch, mix the starch and aromatic acid suspension evenly, the starch structure swells and breaks down in the high temperature suspension to form gelatinized starch with paste-like properties, and obtain a mixture of gelatinized starch and aromatic acid.

[0008] S3, the gelatinized starch obtained in step S2 is heated and pre-calcined with an aromatic acid mixture to obtain a precursor;

[0009] S4, the precursor obtained in step S3 is crushed, carbonized at high temperature and pulverized by airflow to obtain hard carbon.

[0010] Optionally, in step S1, the aromatic acid includes one or more of benzoic acid, methylbenzoic acid, phenylacetic acid, methylphenylacetic acid, terephthalic acid, isophthalic acid, terephthalic acid, phthalic acid, pyromellitic acid, and pyromellitic acid.

[0011] Optionally, in step S1, the solvent is a mixture of deionized water and an organic solvent. The organic solvent is selected from one or more of ethanol, methanol, acetone and glacial acetic acid. The mass ratio of water to organic solvent is 1:0.01 to 0.03, preferably 1:0.01 to 0.02.

[0012] Optionally, in step S1, the mass ratio of the aromatic acid to the solvent is 1:1.0 to 2.3. After the aromatic acid is added to the solvent, it is ground by ball milling, sand milling, or roller milling to obtain an aromatic acid suspension. The particle size range of the solid phase material in the suspension is 0.01 to 20 μm, preferably 0.01 to 8 μm.

[0013] Optionally, in step S2, the aromatic acid suspension obtained in step S1 is heated to 50-90°C, preferably 55-80°C, under stirring conditions, and then starch is added, with a mass ratio of starch to aromatic acid of 2.3-6:1; then the mixture is stirred and mixed for 1-6 hours, preferably 2-4 hours, during which the starch granules swell and break down to form gelatinized starch with paste-like properties. After uniform mixing, a viscoelastic mixture of gelatinized starch and aromatic acid is obtained.

[0014] Optionally, in step S2, the starch includes amylose or amylopectin, or a mixture of both, and may be selected from corn starch, rice starch, potato starch, tapioca starch, wheat starch or other biomass-derived starch.

[0015] Optionally, in step S3, the gelatinized starch and aromatic acid mixture undergo a mixing and heating reaction. The gelatinized starch and aromatic acid mixture is placed in a stirred mixing reactor and stirred and mixed at 120–220°C, preferably 150–200°C, for 1–16 hours, preferably 2–12 hours. Then, the temperature is further increased to 240–320°C for a pre-calcination reaction for 0.5–5 hours. The stirring and mixing speed during the entire mixing and heating reaction and pre-calcination reaction is 70–300 r / min. After the reaction is completed, the mixture is naturally cooled to room temperature to obtain the precursor.

[0016] Optionally, in step S4, the precursor obtained in step S3 is crushed to a powder particle size of 10–74 μm, and then subjected to high-temperature carbonization calcination. The calcination conditions are as follows: from room temperature, the temperature is increased at 5–15 °C / min, preferably 6–12 °C / min, to 800–1000 °C, preferably 850–950 °C, and then increased at 1–10 °C / min, preferably 2–8 °C / min, to 1200–1600 °C, preferably 1300–1500 °C, held at this temperature for 0.5–6 h, preferably 1–4 h, and then naturally cooled to room temperature to complete the high-temperature carbonization. The atmosphere used is nitrogen and / or argon. The material after high-temperature carbonization is then pulverized by airflow to achieve a particle size of 1–10 μm, ultimately yielding hard carbon.

[0017] Secondly, this application provides hard carbon materials prepared by the above-mentioned preparation method.

[0018] Optionally, the hard carbon material is used as an active material to prepare coin half-cells with sodium metal, and the specific capacity is tested to be 300-410 mAh / g, preferably 340-410 mAh / g.

[0019] The hard carbon material has a pore size distribution range of 0.1–20 nm, an average pore size range of 0.3–8 nm, and a specific surface area of ​​1–30 m². 2 / g, closed-cell volume 0.1~0.5cm³ 3 / g.

[0020] Thirdly, this application provides the application of the aforementioned hard carbon material as an active material for the negative electrode.

[0021] Fourthly, this application provides the application of the aforementioned hard carbon material in the preparation of sodium-ion batteries.

[0022] The method for preparing hard carbon provided in this application involves refining aromatic acid particles, gelatinizing starch using a high-temperature solvent, mixing and reacting the starch with the aromatic acid under heat, and then performing esterification, cross-linking, and polymerization with the aromatic acid. Further heating is then used to obtain a precursor, which is subsequently carbonized at high temperature to obtain hard carbon. When the hard carbon material prepared in this application is used as a negative electrode in sodium-ion batteries, it exhibits excellent performance.

[0023] The hard carbon prepared by the method provided in this application was used for battery performance evaluation. The main evaluation method is as follows: Hard carbon was used as the negative electrode active material, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were added as binders, and conductive carbon black was added as a conductive agent. The ratio of each substance was hard carbon:CMC:SBR:conductive carbon black = 94:2:2:2. Deionized water was used as a solvent to prepare a uniform slurry, which was then coated onto aluminum foil. After drying, an electrode sheet was obtained. The dry matter loading on the aluminum foil was 2 mg / cm³. 2 A coin cell was fabricated using sodium metal using the prepared electrode sheet, and its performance was then tested. The test conditions were as follows: discharge at a constant rate until the battery voltage ≤ 0V, let stand for 5 minutes, and then charge at a constant rate until the battery voltage ≥ 2.5V. The initial coulombic efficiency, specific capacity at 0.1C rate, specific capacity at 0.2C rate, and capacity retention rate after 500 cycles at 1C rate (specific capacity at the 500th cycle compared to the specific capacity at the first cycle) were obtained.

[0024] Compared with the prior art, this application provides a method for preparing hard carbon by esterifying starch. The method involves refining aromatic acid particles, gelatinizing starch with a high-temperature solvent and mixing it with aromatic acid, then esterifying and cross-linking the active hydroxyl groups in the starch molecules with the carboxylic acid groups in the aromatic acid, further heating the reaction to obtain a precursor, and then carbonizing it at high temperature to obtain hard carbon.

[0025] The method provided in this application mainly includes the following beneficial effects:

[0026] (1) The aromatic acid particles are refined to the submicron level, which can significantly improve the esterification reaction between aromatic acid and starch, and obtain a more complex cross-linked structure. This can introduce abundant C=O groups and aromatic ring structures into the precursor, so that carbon atoms can be effectively prevented from forming an ordered graphite layer crystal structure during high-temperature carbonization. The hard carbon obtained is longer curled graphite microcrystals, forming more micropores and having a larger closed pore volume.

[0027] (2) After the heating reaction, the reaction is further heated, and the reactants can be decomposed and foamed in a controlled manner to obtain the precursor. This process helps hard carbon to form abundant defects and pores, and can form abundant micropores and closed pore structures during high-temperature carbonization.

[0028] (3) The method provided in this application uses starch as the main raw material, which has low raw material cost and is suitable for large-scale production. The prepared hard carbon has advantages such as low specific surface area, large closed pore volume, high specific capacity, high initial coulombic efficiency, and good cycle stability. When the hard carbon prepared by this method is used as a negative electrode active material in sodium-ion batteries, it exhibits excellent performance. Attached Figure Description

[0029] Figure 1 Transmission electron microscope image of the hard carbon material prepared in Example 1.

[0030] Figure 2 Transmission electron microscope image of the hard carbon material prepared for Comparative Example 1. Detailed Implementation

[0031] The present application is further illustrated below with reference to specific embodiments. The following descriptions are merely a few embodiments of the present application and are not intended to limit the present application in any way. Although the present application discloses preferred embodiments as follows, they are not intended to limit the present application. Any modifications or variations made by those skilled in the art without departing from the scope of the technical solution of the present application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

[0032] Unless otherwise specified, the raw materials used in the embodiments of this application are all purchased commercially and used directly without any special treatment.

[0033] Unless otherwise specified, the analytical methods in the embodiments all adopt conventional instrument or equipment settings and conventional analytical methods.

[0034] Example 1

[0035] (1) Using methylbenzoic acid as the aromatic acid, weigh 100g of methylbenzoic acid and add 180g of a mixed solvent of water and ethanol, with a mass ratio of water to ethanol of 1:0.015. Then, grind the mixture using a sand mill and use a laser particle size analyzer to test the particle size range of the solid material in the ground suspension. Grind until the particle size range of the solid material in the aromatic acid suspension reaches 0.02 to 8μm to obtain the aromatic acid suspension.

[0036] (2) The aromatic acid suspension obtained in step (1) was heated to 70°C under stirring, and then 300g of corn starch (purchased from Shandong Binzhou Jinhui Corn Development Co., Ltd.) was added and stirred for 3 hours to obtain a mixture of gelatinized starch and aromatic acid.

[0037] (3) The gelatinized starch and aromatic acid mixture described in step (2) is placed into a stirred mixing reactor and stirred and mixed at 180°C for 3 hours. Then the temperature is raised to 250°C and the pre-calcination reaction is continued for 2 hours. The stirring speed is 200 r / min throughout the process. After the reaction is completed, it is naturally cooled to room temperature to obtain the precursor.

[0038] (4) The esterified starch pre-calcined precursor described in step (3) is crushed until the powder particle size reaches 20-74 μm. Then, it is subjected to high-temperature carbonization calcination. The calcination conditions are: heating from room temperature to 900℃ at 8℃ / min, then further heating to 1350℃ at 5℃ / min, holding at this temperature for 1.5 hours, and then naturally cooling to complete the high-temperature carbonization. The atmosphere used in the high-temperature carbonization process is nitrogen. The sample after high-temperature carbonization is pulverized by airflow to achieve a particle size of 1-10 μm, ultimately obtaining hard carbon.

[0039] The physicochemical properties of the hard carbon obtained in Example 1 were tested, including the specific surface area, average micropore size, pore volume, and closed pore volume of the hard carbon powder.

[0040] The performance of the hard carbon battery obtained in Example 1 was tested, including initial coulombic efficiency, specific capacity at 0.1C rate, specific capacity at 0.2C rate, and capacity retention after 500 cycles at 1C rate. The electrode preparation conditions were as follows: hard carbon was used as the negative electrode active material, with carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) added as binders, and conductive carbon black as a conductive agent. The ratio of each material was hard carbon:CMC:SBR:conductive carbon black = 94:2:2:2. Deionized water was used as the solvent to prepare a uniform slurry, which was then coated onto aluminum foil. After drying, the electrode sheet was obtained, with a dry matter loading of 2 mg / cm³ on the aluminum foil. 2 The prepared electrode sheets were used to prepare coin cells of sodium metal, and then the performance was tested. The test conditions were as follows: discharge at a constant rate to the battery voltage ≤0V, let stand for 5 minutes, and then charge at a constant rate to the battery voltage ≥2.5V.

[0041] Example 2

[0042] The process and conditions are the same as in Example 1, except that the aromatic acid used in this example is terephthalic acid, and step (1) is different, as follows:

[0043] (1) Use terephthalic acid as an aromatic acid, weigh 100g of terephthalic acid.

[0044] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 2 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0045] Example 3

[0046] The process and conditions are the same as in Example 1, except that the aromatic acid used in this example is isophthalic acid, and step (1) is different, as follows:

[0047] (1) Use isophthalic acid as an aromatic acid, weigh 100g of isophthalic acid.

[0048] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 2 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0049] Example 4

[0050] The process and conditions are the same as in Example 1, except that in this example, the particle size of the solid material in the aromatic acid suspension is ground until it reaches 0.02–15 μm to obtain the aromatic acid suspension. Step (1) is different, as follows:

[0051] (1) Using methylbenzoic acid as the aromatic acid, weigh 100g of methylbenzoic acid and add 180g of a mixed solvent of water and ethanol, with a mass ratio of water to ethanol of 1:0.015. Then, grind the mixture using a sand mill and use a laser particle size analyzer to test the particle size range of the solid material in the ground suspension. Grind until the particle size range of the solid material in the aromatic acid suspension reaches 0.02 to 15μm to obtain the aromatic acid suspension.

[0052] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 4 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0053] Example 5

[0054] The process and conditions are the same as in Example 1, except that in this example, the particle size of the solid material in the aromatic acid suspension is ground until it reaches 0.01–5 μm to obtain the aromatic acid suspension. Step (1) is different, as follows:

[0055] (1) Using methylbenzoic acid as an aromatic acid, weigh 100g of methylbenzoic acid and add 180g of a mixed solvent of water and ethanol, with a mass ratio of water to ethanol of 1:0.015. Then, grind the mixture using a sand mill and use a laser particle size analyzer to test the particle size range of the solid material in the ground suspension. Grind until the particle size range of the solid material in the aromatic acid suspension reaches 0.01 to 5μm to obtain the aromatic acid suspension.

[0056] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 5 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0057] Example 6

[0058] The process and conditions are the same as in Example 1, except that the mass of the mixed solvent of water and ethanol added in this example is different, and step (1) in the implementation step is different, as follows:

[0059] (1) Add 120g of a mixed solvent of water and ethanol, with a mass ratio of water to ethanol of 1:0.015.

[0060] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 6 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0061] Example 7

[0062] The process and conditions are the same as in Example 1, except that the mass of the mixed solvent of water and ethanol added in this example is different, and step (1) in the implementation step is different, as follows:

[0063] (1) Add 220g of a mixed solvent of water and ethanol, with a mass ratio of water to ethanol of 1:0.015.

[0064] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 7 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0065] Example 8

[0066] The process and conditions are the same as in Example 1, except that the ratio of water to ethanol in the water and ethanol mixed solvent added in this example is different, and step (1) in the implementation step is different, as follows:

[0067] (1) Add 180g of a mixed solvent of water and ethanol, with a mass ratio of water to ethanol of 1:0.01.

[0068] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 8 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0069] Example 9

[0070] The process and conditions are the same as in Example 1, except that the amount of starch used is different in this example, and step (2) is different, as follows:

[0071] (2) The aromatic acid suspension obtained in step (1) was heated to 70°C under stirring, and then 400g of corn starch (purchased from Shandong Binzhou Jinhui Corn Development Co., Ltd.) was added and stirred for 3 hours to obtain a mixture of gelatinized starch and aromatic acid.

[0072] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 9 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0073] Example 10

[0074] The process and conditions are the same as in Example 1, except that the amount of starch used is different in this example, and step (2) is different, as follows:

[0075] (2) The aromatic acid suspension obtained in step (1) was heated to 70°C under stirring, and then 500g of corn starch (purchased from Shandong Binzhou Jinhui Corn Development Co., Ltd.) was added and stirred for 3 hours to obtain a mixture of gelatinized starch and aromatic acid.

[0076] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 10 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0077] Example 11

[0078] The process and conditions are the same as in Example 1, except that the heating temperature of the mixture of gelatinized starch and aromatic acid is different in this example, and step (3) is different, as follows:

[0079] (3) The gelatinized starch and aromatic acid mixture described in step (2) is placed into a stirred mixing reactor and stirred and mixed at 160°C for 8 hours. Then the temperature is raised to 250°C and the pre-calcination reaction is continued for 2 hours. The stirring speed is 200 r / min throughout the process. After the reaction is completed, it is naturally cooled to room temperature to obtain the precursor.

[0080] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 11 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0081] Example 12

[0082] The process and conditions are the same as in Example 1, except that the heating temperature of the mixture of gelatinized starch and aromatic acid is different in this example, and step (3) is different, as follows:

[0083] (3) The gelatinized starch and aromatic acid mixture described in step (2) is placed into a stirred mixing reactor and stirred and mixed at 200°C for 2 hours. Then the temperature is raised to 250°C and the pre-calcination reaction is continued for 2 hours. The stirring speed is 200 r / min throughout the process. After the reaction is completed, it is naturally cooled to room temperature to obtain the precursor.

[0084] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 12 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0085] Example 13

[0086] The process and conditions are the same as in Example 1, except that the pre-calcination temperature of the mixture of gelatinized starch and aromatic acid is different in this example, and step (3) is different in the implementation steps, as follows:

[0087] (3) The gelatinized starch and aromatic acid mixture described in step (2) is placed into a stirred mixing reactor and stirred and mixed at 180°C for 3 hours. Then the temperature is raised to 270°C and the pre-calcination reaction is continued for 2 hours. The stirring speed is 200 r / min throughout the process. After the reaction is completed, it is naturally cooled to room temperature to obtain the precursor.

[0088] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 13 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0089] Example 14

[0090] The process and conditions are the same as in Example 1, except that the pre-calcination temperature of the mixture of gelatinized starch and aromatic acid is different in this example, and step (3) is different in the implementation steps, as follows:

[0091] (3) The gelatinized starch and aromatic acid mixture described in step (2) is placed into a stirred mixing reactor and stirred and mixed at 180°C for 3 hours. Then the temperature is raised to 300°C and the pre-calcination reaction is continued for 2 hours. The stirring speed is 200 r / min throughout the process. After the reaction is completed, it is naturally cooled to room temperature to obtain the precursor.

[0092] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 14 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0093] Example 15

[0094] The process and conditions are the same as in Example 1, except that the pre-calcination time of the mixture of gelatinized starch and aromatic acid is different in this example, and step (3) is different in the implementation steps, as follows:

[0095] (3) The gelatinized starch and aromatic acid mixture described in step (2) is placed into a stirred mixing reactor and stirred and mixed at 180°C for 3 hours. Then the temperature is raised to 250°C and the pre-calcination reaction is continued for 4 hours. The stirring speed is 200 r / min throughout the process. After the reaction is completed, it is naturally cooled to room temperature to obtain the precursor.

[0096] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 15 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0097] Example 16

[0098] The process and conditions are the same as in Example 1, except that the high-temperature roasting temperature is different in this example, and step (4) is different, as follows:

[0099] (4) The esterified starch pre-calcined precursor described in step (3) is crushed until the powder particle size reaches 20-74 μm. Then, it is subjected to high-temperature carbonization calcination. The calcination conditions are: heating from room temperature to 900℃ at 8℃ / min, then continuing to heat to 1450℃ at 5℃ / min, holding at this temperature for 1.5 hours, and then naturally cooling to complete the high-temperature carbonization. The atmosphere used in the high-temperature carbonization process is nitrogen. The sample after high-temperature carbonization is pulverized by airflow to make the material particle size reach 1-10 μm, finally obtaining hard carbon.

[0100] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 16 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0101] Example 17

[0102] The process and conditions are the same as in Example 1, except that the high-temperature roasting and heat preservation time is different in this example, and step (4) is different, as follows:

[0103] (4) The esterified starch pre-calcined precursor described in step (3) is crushed until the particle size reaches 20-74 μm. Then, it is subjected to high-temperature carbonization calcination. The calcination conditions are: heating from room temperature to 900℃ at 8℃ / min, then further heating to 1350℃ at 5℃ / min, holding at that temperature for 3 hours, and then naturally cooling to complete the high-temperature carbonization. The atmosphere used in the high-temperature carbonization process is nitrogen. The sample after high-temperature carbonization is pulverized by airflow to make the particle size reach 1-10 μm, finally obtaining hard carbon.

[0104] The remaining steps are the same as in Example 1. The hard carbon prepared in Example 17 is used to test the physicochemical properties and battery performance. The test content and conditions are the same as in Example 1.

[0105] Comparative Example 1

[0106] The process and conditions are the same as in Example 1, except that the aromatic acid methyl benzoic acid is not ground in step (1) of this comparative example, as follows:

[0107] (1) Using methylbenzoic acid as an aromatic acid, weigh 100g of methylbenzoic acid and add 180g of a mixed solvent of water and ethanol, with a mass ratio of water to ethanol of 1:0.015. Then stir evenly and use a laser particle size analyzer to test the particle size range of the solid material in the ground suspension. The particle size range of the solid material in the aromatic acid suspension reaches 70-200μm.

[0108] The remaining steps are the same as in Example 1. The hard carbon prepared in Comparative Example 1 is used to test the physicochemical properties and battery performance. The test conditions and contents are the same as in Example 1.

[0109] Comparative Example 2

[0110] The process and conditions are the same as in Example 1, except that in step (1) of this comparative example, the aromatic acid methyl benzoic acid was not ground to a smaller size, as detailed below:

[0111] (1) Using methylbenzoic acid as an aromatic acid, 100g of methylbenzoic acid was weighed and added to a mixed solvent of 180g of water and ethanol, with a mass ratio of water to ethanol of 1:0.015. Then, the mixture was ground using a ball mill, and the particle size range of the solid material in the ground suspension was tested using a laser particle size analyzer. The particle size range of the solid material in the aromatic acid suspension reached 35-100μm.

[0112] The remaining steps are the same as in Example 1. The hard carbon prepared in Comparative Example 2 is used to test the physicochemical properties and battery performance. The test conditions and contents are the same as in Example 1.

[0113] Comparative Example 3

[0114] The process and conditions are the same as in Example 1, except that in step (1) of this comparative example, the aromatic acid methyl benzoic acid was not ground to a smaller size, as detailed below:

[0115] (1) Using methylbenzoic acid as an aromatic acid, 100g of methylbenzoic acid was weighed and added to a mixed solvent of 180g of water and ethanol, with a mass ratio of water to ethanol of 1:0.015. Then, the mixture was ground using a ball mill, and the particle size range of the solid material in the suspension after grinding was tested using a laser particle size analyzer. The particle size range of the solid material in the aromatic acid suspension reached 25-74μm.

[0116] The remaining steps are the same as in Example 1. The hard carbon prepared in Comparative Example 3 is used to test the physicochemical properties and battery performance. The test conditions and contents are the same as in Example 1.

[0117] Comparative Example 4

[0118] The process and conditions are the same as in Example 1, except that the mass ratio of water and ethanol in step (1) of this comparative example is different, as detailed below:

[0119] (1) Using methylbenzoic acid as an aromatic acid, weigh 100g of methylbenzoic acid and add 180g of a mixed solvent of water and ethanol. The mass ratio of water to ethanol is 1:0.05.

[0120] The remaining steps are the same as in Example 1. The hard carbon prepared in Comparative Example 4 is used to test the physicochemical properties and battery performance. The test conditions and contents are the same as in Example 1.

[0121] Comparative Example 5

[0122] The process and conditions are the same as in Example 1, except that in step (2) of this comparative example, the aromatic acid suspension is starched at room temperature, as follows:

[0123] (2) Add 300g of corn starch (purchased from Shandong Binzhou Jinhui Corn Development Co., Ltd.) to the aromatic acid suspension obtained in step (1) at room temperature of 25°C, stir and mix for 3h to obtain a mixture of starch and aromatic acid.

[0124] The remaining steps are the same as in Example 1. The hard carbon prepared in Comparative Example 5 is used to test the physicochemical properties and battery performance. The test conditions and contents are the same as in Example 1.

[0125] Comparative Example 6

[0126] The process and conditions are the same as in Example 1, except that in step (2) of this comparative example, the heating temperature of the aromatic acid suspension is 40°C, as detailed below:

[0127] (2) The aromatic acid suspension obtained in step (1) was heated to 40°C under stirring, and 300g of corn starch (purchased from Shandong Binzhou Jinhui Corn Development Co., Ltd.) was added. The mixture was stirred for 3 hours to obtain a starch and aromatic acid mixture.

[0128] The remaining steps are the same as in Example 1. The hard carbon prepared in Comparative Example 6 is used to test the physicochemical properties and battery performance. The test conditions and contents are the same as in Example 1.

[0129] Comparative Example 7

[0130] The process and conditions are the same as in Example 1, except that in step (3) of this comparative example, the mixing and heating temperature of the gelatinized starch and aromatic acid mixture is different, as detailed below:

[0131] (3) The gelatinized starch and aromatic acid mixture described in step (2) is placed into a stirred mixing reactor and stirred and mixed at 100°C for 3 hours. Then the temperature is raised to 250°C and the pre-calcination reaction is continued for 2 hours. The stirring speed is 200 r / min throughout the process. After the reaction is completed, it is naturally cooled to room temperature to obtain the precursor.

[0132] The remaining steps are the same as in Example 1. The hard carbon prepared in Comparative Example 7 is used to test the physicochemical properties and battery performance. The test conditions and contents are the same as in Example 1.

[0133] Comparative Example 8

[0134] The process and conditions are the same as in Example 1, except that in step (3) of this comparative example, the mixing and heating temperature of the gelatinized starch and aromatic acid mixture is different, as detailed below:

[0135] (3) The gelatinized starch and aromatic acid mixture described in step (2) is placed into a stirred mixing reactor and stirred and mixed at 250°C for 3 hours. Then, a pre-calcination reaction is carried out at 250°C for 2 hours. The stirring speed is 200 r / min throughout the process. After the reaction is completed, the mixture is naturally cooled to room temperature to obtain the precursor.

[0136] The remaining steps are the same as in Example 1. The hard carbon prepared in Comparative Example 8 is used to test the physicochemical properties and battery performance. The test conditions and contents are the same as in Example 1.

[0137] Comparative Example 9

[0138] The process and conditions are the same as in Example 1. The difference is that in step (3) of this comparative example, the pre-calcination temperature is different after the gelatinized starch and aromatic acid mixture are mixed and heated to react. The details are as follows:

[0139] (3) The gelatinized starch and aromatic acid mixture described in step (2) is placed into a stirred mixing reactor and stirred and mixed at 180°C for 3 hours. Then, a pre-calcination reaction is carried out at 220°C for 2 hours. The stirring speed is 200 r / min throughout the process. After the reaction is completed, the mixture is naturally cooled to room temperature to obtain the precursor.

[0140] The remaining steps are the same as in Example 1. The hard carbon prepared in Comparative Example 9 is used to test the physicochemical properties and battery performance. The test conditions and contents are the same as in Example 1.

[0141] Comparative Example 10

[0142] The process and conditions are the same as in Example 1. The difference is that in step (3) of this comparative example, the pre-calcination temperature is different after the gelatinized starch and aromatic acid mixture are mixed and heated to react. The details are as follows:

[0143] (3) The gelatinized starch and aromatic acid mixture described in step (2) is placed into a stirred mixing reactor and stirred and mixed at 180°C for 3 hours. Then, a pre-calcination reaction is carried out at 350°C for 2 hours. The stirring speed is 200 r / min throughout the process. After the reaction is completed, the mixture is naturally cooled to room temperature to obtain the precursor.

[0144] The remaining steps are the same as in Example 1. The hard carbon prepared in Comparative Example 9 is used to test the physicochemical properties and battery performance. The test conditions and contents are the same as in Example 1.

[0145] Comparative Example 11

[0146] The process and conditions are the same as in Example 1. The difference is that in step (3) of this comparative example, the pre-calcination time is different after the gelatinized starch and aromatic acid mixture are mixed and heated. The details are as follows:

[0147] (3) The gelatinized starch and aromatic acid mixture described in step (2) is placed into a stirred mixing reactor and stirred and mixed at 180°C for 3 hours. Then, the mixture is pre-calcined at 250°C for 7 hours. The stirring speed is 200 r / min throughout the process. After the reaction is completed, the mixture is naturally cooled to room temperature to obtain the precursor.

[0148] The remaining steps are the same as in Example 1. The hard carbon prepared in Comparative Example 10 is used to test the physicochemical properties and battery performance. The test conditions and contents are the same as in Example 1.

[0149] Table 1 shows the test results of the physicochemical properties and battery performance of the hard carbon batteries in Examples 1-17 and Comparative Examples 1-11. The physicochemical properties of the hard carbon powder were tested for specific surface area, pore volume, and closed-cell volume. The battery performance was tested for the initial coulombic efficiency at 0.1C, the specific capacity at 0.1C, and the capacity retention after 500 cycles at 1C.

[0150] The electrode preparation conditions were as follows: hard carbon was used as the negative electrode active material, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were added as binders, and conductive carbon black was used as a conductive agent. The ratio of each material was hard carbon:CMC:SBR:conductive carbon black = 94:2:2:2. Deionized water was used as the solvent to prepare a uniform slurry, which was then coated onto aluminum foil. After drying, the electrode sheet was obtained. The dry matter loading on the aluminum foil was 2 mg / cm³. 2 .

[0151] A coin cell was prepared using the prepared hard carbon electrode sheet to fabricate sodium metal, and then its performance was tested. The test conditions were: discharge at a constant rate until the battery voltage ≤ 0V, let stand for 5 minutes, and then charge at a constant rate until the battery voltage ≥ 2.5V.

[0152] The hard carbon prepared in Example 1 and Comparative Example 1 was characterized and analyzed for its microstructure using transmission electron microscopy. Figure 1 The image shown is a transmission electron microscope (TEM) image of the hard carbon material prepared in Example 1. Figure 2The image shown is a transmission electron microscope (TEM) image of the hard carbon prepared in Comparative Example 1. Comparative analysis reveals that the hard carbon material prepared in Example 1 using the method of this invention exhibits significantly more disordered, curled, layered carbon lattice fringes and abundant closed-pore structures, resulting in a higher sodium storage capacity. In contrast, the hard carbon prepared in Comparative Example 1 displays more ordered carbon lattice fringes. It is known that hard carbon materials with high disordered, curled carbon lattice fringes and abundant closed-pore structures exhibit superior performance and are more suitable for use as anode active materials in sodium-ion batteries. Hard carbon materials with ordered, straight carbon lattice fringes have a microstructure more inclined towards the graphite phase, resulting in poorer performance as anode active materials in sodium-ion batteries. Specifically, the hard carbon with a regular and ordered carbon microcrystalline phase exhibits lower specific capacity and poorer rate performance.

[0153] Therefore, in comparison with the appendix Figure 1 and attached Figure 2 This indicates that the method for preparing hard carbon from lignin resin provided by the present invention produces hard carbon with a superior carbon microcrystalline structure and superior performance, achieving the beneficial effects of high performance and low cost.

[0154] Table 1 Comparison of performance test results of hard carbon materials in the examples and comparative examples

[0155]

[0156]

[0157] Comparative analysis of the examples and comparative examples shows that, under optimal conditions, the finer the particle size of the aromatic acid, the higher the closed-cell volume of the prepared hard carbon, resulting in excellent sodium storage performance. The specific capacity reaches 366.9 mAh / g, with an initial coulombic efficiency of 93.1% and a capacity retention rate exceeding 91.0% after 500 cycles at 1C. Examples 1-3 demonstrate that different aromatic acids, when ground to reduce particle size, can all produce high-performance hard carbon materials. Comparing Examples 1 and 4-5, as the particle size of the aromatic acid decreases, the closed-cell volume of the hard carbon gradually increases, and the specific capacity also gradually improves, both reaching high values. The amount of mixed solvent has a certain impact on the gelatinization effect of starch. Comparing Examples 1 and 6-7 shows that increasing the amount of mixed solvent increases the specific surface area of ​​the hard carbon. After the specific capacity reaches a certain value, further increasing the amount of mixed solvent results in a smaller change in specific capacity. Comparing Examples 1, 11-12, and Comparative Example 8, it can be seen that the mixing and heating reaction process plays a crucial role in the performance of hard carbon. Adjusting the mixing and heating reaction temperature and time can yield hard carbon with excellent performance. However, in Comparative Example 8, the mixing and heating reaction temperature reached the pre-calcination temperature, resulting in a significant increase in the specific surface area of ​​the prepared hard carbon, a significant decrease in the closed-cell volume, a decrease in initial efficiency and specific capacity, and poor cycle stability. Analysis of Comparative Examples 9-11 shows that the optimal temperature and time of the pre-calcination process have beneficial effects on the performance of hard carbon. Excessively high pre-calcination temperatures lead to a significant increase in the specific surface area of ​​the hard carbon, a decrease in the closed-cell volume, and a decrease in initial efficiency and specific capacity. Conversely, excessively low pre-calcination temperatures result in no controllable decomposition and foaming of the sample, a low closed-cell volume, and although the initial efficiency is relatively high, the specific capacity is low.

[0158] In summary, this application uses starch as a raw material, which has low raw material cost and a simple manufacturing process, significantly reducing the cost of the prepared hard carbon material. By refining aromatic acid particles, starch is gelatinized using a heated solvent and uniformly mixed with the aromatic acid. Then, the active hydroxyl groups in the starch molecules undergo cross-linking polymerization with the carboxylic acid groups in the aromatic acid, forming a complex cross-linked structure with aromatic rings as nodes. Further heating yields the precursor, which is then carbonized at high temperature to obtain hard carbon. The cross-linking polymerization process introduces abundant C=O groups and aromatic ring structures into the precursor molecular structure, effectively preventing the formation of an ordered graphite layer crystal structure during high-temperature carbonization. The resulting hard carbon has a longer, coiled, disordered carbon layer, resulting in high specific capacity and high initial coulombic efficiency.

[0159] The above description is merely an embodiment of this application and does not constitute any limitation on this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing hard carbon from biomass materials, characterized in that: Includes the following steps: S1, Aromatic acid is placed in a solvent and ground to obtain an aromatic acid suspension; S2, Heat the aromatic acid suspension obtained in step S1, then add starch, mix the starch and aromatic acid suspension evenly, the starch structure swells and breaks down in the high temperature suspension to form gelatinized starch with paste-like properties, and obtain a mixture of gelatinized starch and aromatic acid. S3, the gelatinized starch obtained in step S2 is heated and pre-calcined with an aromatic acid mixture to obtain a precursor; S4, the precursor obtained in step S3 is crushed, carbonized at high temperature and pulverized by airflow to obtain hard carbon.

2. The method according to claim 1, characterized in that: In step S1, the aromatic acid includes at least one or more of benzoic acid, methylbenzoic acid, phenylacetic acid, methylphenylacetic acid, terephthalic acid, isophthalic acid, terephthalic acid, phthalic acid, pyromellitic acid, and pyromellitic acid. The solvent is a mixture of deionized water and an organic solvent. The organic solvent is selected from one or more of ethanol, methanol, acetone and glacial acetic acid. The mass ratio of water to organic solvent is 1:0.01 to 0.03, preferably 1:0.01 to 0.

02. The mass ratio of aromatic acid to solvent is 1:1.0 to 2.

3. After the aromatic acid is added to the solvent, it is ground by ball milling, sand milling, or roller milling to obtain an aromatic acid suspension. The particle size range of the solid phase material in the suspension is 0.01 to 20 μm, preferably 0.01 to 8 μm.

3. The method according to claim 1, characterized in that: In step S2, the aromatic acid suspension obtained in step S1 is heated to 50-90°C, preferably 55-80°C, under stirring conditions, and then starch is added, with a mass ratio of starch to aromatic acid of 2.3-6:1; then the mixture is stirred for 1-6 hours, preferably 2-4 hours, and the starch granules swell and break down to form gelatinized starch with paste-like properties. After uniform mixing, a viscoelastic mixture of gelatinized starch and aromatic acid is obtained. In step S2, the starch includes amylose or amylopectin, or a mixture of both, and may be selected from corn starch, rice starch, potato starch, tapioca starch, wheat starch or other biomass-derived starch.

4. The method according to claim 1, characterized in that: In step S3, the gelatinized starch and aromatic acid mixture undergo a mixing and heating reaction. The gelatinized starch and aromatic acid mixture is placed in a stirred mixing reactor and stirred and mixed at 120-220°C, preferably 150-200°C, for 1-16 hours, preferably 2-12 hours. Then, the temperature is further increased to 240-320°C for a pre-calcination reaction for 0.5-5 hours. The stirring and mixing speed is 70-300 r / min throughout the mixing, heating, and pre-calcination reactions. After the reaction is completed, the mixture is naturally cooled to room temperature to obtain the precursor.

5. The method according to claim 1, characterized in that: In step S4, the precursor obtained in step S3 is crushed until the powder particle size reaches 10-74 μm, and then subjected to high-temperature carbonization calcination. The calcination conditions are as follows: from room temperature, the temperature is increased to 800-1000℃, preferably 850-950℃, at a rate of 5-15℃ / min, preferably 6-12℃ / min; then, the temperature is increased to 1200-1600℃, preferably 1300-1500℃, at a rate of 1-10℃ / min, preferably 2-8℃ / min; the temperature is held for 0.5-6h, preferably 1-4h; and then the temperature is naturally cooled to room temperature to complete the high-temperature carbonization. The atmosphere used is nitrogen and / or argon atmosphere. After high-temperature carbonization, the material is pulverized by airflow to achieve a particle size of 1–10 μm, ultimately yielding hard carbon.

6. A hard carbon material prepared by the method according to any one of claims 1-5.

7. The hard carbon material according to claim 6, characterized in that: Using hard carbon as the active material to prepare coin half-cells with sodium metal, the specific capacity was tested to be 300-410 mAh / g, preferably 340-410 mAh / g.

8. The hard carbon material according to claim 6, characterized in that: The hard carbon material has a pore size distribution range of 0.1–20 nm, an average pore size range of 0.3–8 nm, and a specific surface area of ​​1–30 m². 2 / g, closed-cell volume 0.1~0.5cm³ 3 / g.

9. The application of the hard carbon material of claim 6 as a negative electrode active material in a sodium-ion battery.

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