Starch-coated hard carbon negative electrode material, preparation method thereof and sodium ion battery

Abstract

The application relates to the technical field of battery material preparation, and provides a starch-coated hard carbon negative material, a preparation method thereof and a sodium ion battery. The preparation method of the starch-coated hard carbon negative material comprises the following steps: (1) a hard carbon precursor is pre-carbonized, crushed and once-carbonized to obtain hard carbon powder; (2) the hard carbon powder is uniformly mixed with starch to obtain mixed powder, a starch modifier is dissolved in a solvent to form a modified solution, the modified solution is reacted with the mixed powder, and the modified solution is dried to obtain a modified precursor, wherein the starch modifier comprises amine organic matter and ester organic matter; and (3) the modified precursor is twice-carbonized and sieved. The starch-coated hard carbon negative material prepared by the application has a reduced specific surface area and a suitable closed pore structure, has a high initial coulombic efficiency and specific capacity when used in a sodium ion battery, and can effectively improve the rate performance and cycle performance.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, and in particular to starch-coated hard carbon anode materials and their preparation methods, as well as sodium-ion batteries. Background Technology

[0002] In today's society, which pursues new energy sources and carbon neutrality, electrochemical energy storage has become a global research focus. Sodium-ion batteries have advantages such as wide availability of raw materials, low cost, and good overall performance, and are not limited by lithium resources, making them more suitable for large-scale energy storage needs. However, because sodium-ion batteries cannot form stable compounds with traditional lithium-ion battery graphite anode materials during charging and discharging, the availability of ideal anode materials has become one of the reasons limiting the development of sodium-ion batteries. Hard carbon, a carbon material that is difficult to graphitize above 2500℃, has become the most ideal anode material for sodium batteries due to its high sodium storage capacity, potential stability, small volume deformation after sodium intercalation, and good low-temperature and fast-charging performance.

[0003] Currently, biomass, coal, and resins, such as microcrystalline cellulose, rice husks, bituminous coal, and phenolic resins, have been converted into a series of starch-coated hard carbon anode materials for sodium-ion batteries. However, due to the inherent complexity of the precursor due to the coexistence of multiple components, these components decompose at different temperatures through specific mechanisms during carbonization, interacting with each other and resulting in a porous structure in the hard carbon material. This porous structure leads to a high specific surface area, low capacity and initial efficiency, and a relatively low battery energy density. To improve the application of hard carbon as a sodium-ion anode material, coating is currently an effective method. Commonly used coating methods include chemical vapor deposition, hydrothermal methods, and polymer coating; however, these processes are relatively complex, with high production costs, low yields, and are not conducive to large-scale production. Summary of the Invention

[0004] In view of the above problems, the purpose of this invention is to provide a starch-coated hard carbon anode material, its preparation method, and a sodium-ion battery. The starch-coated hard carbon anode material prepared by this invention has a reduced specific surface area and a suitable closed-pore structure, which results in high initial coulombic efficiency and specific capacity in sodium-ion batteries, effectively improving rate performance and cycle performance.

[0005] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a starch-coated hard carbon anode material, comprising the steps of:

[0006] (1) Hard carbon precursor is pre-carbonized, crushed and carbonized in one step to obtain hard carbon powder;

[0007] (2) Hard carbon powder and starch are mixed evenly to obtain mixed powder. Starch modifier is dissolved in solvent to form a modification solution. The modification solution is then reacted with the mixed powder and dried to obtain a modified precursor. The starch modifier includes amine organic compounds and ester organic compounds.

[0008] (3) The modified precursor is subjected to secondary carbonization and sieving.

[0009] Compared with existing technologies, this invention uses hard carbon material as the main body and modifies starch in situ through starch modifiers. This enables starch to adhere uniformly to the surface of hard carbon, improving the closed-cell structure and uniform distribution of the starch-coated hard carbon anode material after carbonization, thereby enhancing the initial coulombic efficiency and specific capacity. The starch modifiers of this invention include amine organic compounds and ester organic compounds. The amine organic compounds can be grafted onto starch to enhance its swelling properties, resulting in more uniform starch coating on the hard carbon surface. Simultaneously, the grafted nitrogen-containing functional groups increase the content of pyridine and pyrrole nitrogen formed after carbonization, providing more electron transport channels and active sites, thus increasing the conductivity and topological defects of the starch-coated hard carbon anode material. Furthermore, the incorporation of nitrogen-containing functional groups can alter the atomic structure of the graphite carbon edge or bulk phase, thereby improving the battery's rate performance and cycle performance. The introduction of ester organic compounds can form a binder with starch, increasing the adhesion between starch and the hard carbon backbone, providing more closed-cell structures, reducing the specific surface area of ​​hard carbon, and improving the initial coulombic efficiency and specific capacity. Therefore, compared with uncoated hard carbon powder, the starch-coated hard carbon anode material prepared by the method of this invention can improve the first reversible specific capacity at 0.1C by 10 mAh / g to 65 mAh / g, the first coulombic efficiency ≥90.1%, the rate capacity ratio at 1C current by 16.9% to 24.1%, and the capacity retention rate after 300 cycles at 0.5C ≥98.8%.

[0010] In some embodiments, the hard carbon precursor is selected from at least one of biomass, coal, and resin, and is pulverized in an air jet mill, resulting in a particle size Dv 50 of 3 μm to 8 μm and a specific surface area of ​​10 m². 2 / g~200m 2 / g.

[0011] In some implementation schemes, the pre-carbonization temperature is 400℃~700℃, the pre-carbonization time is 0.5h~10h, the primary carbonization temperature is 1100℃~1600℃, and the primary carbonization holding time is 0.5h~10h.

[0012] In some implementations, pre-carbonization, primary carbonization, and secondary carbonization are all carried out in an inert atmosphere, each independently selected from at least one of nitrogen and argon.

[0013] In some implementations, the mass ratio of hard carbon powder to starch is 1:0.05 to 0.5, the mass ratio of amine organics, ester organics and solvent is 0.2 to 0.5:0.5 to 0.8:1.0 to 1.5, and the mass ratio of modified solution to mixed powder is 0.5 to 2:1.

[0014] In some embodiments, the starch is selected from at least one of wheat starch, corn starch and potato starch; the amine organic compound is selected from at least one of acrylamide, ethylenediamine and aniline; the ester organic compound is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate and dicyclohexylmethane diisocyanate; and the solvent is selected from at least one of petroleum ether, ethyl acetate, acetone and tetrahydrofuran.

[0015] In some implementations, the reaction temperature is 50℃~100℃, the reaction time is 1h~10h, the drying temperature is 80℃~250℃, and the drying time is greater than 5h.

[0016] In some implementation schemes, the temperature of secondary carbonization is 900℃~1400℃, the holding time of secondary carbonization is 0.5h~10h, and the mesh size used for sieving is 200 mesh~400 mesh.

[0017] The second aspect of the present invention provides a starch-coated hard carbon anode material, which is prepared by the aforementioned method for preparing starch-coated hard carbon anode materials.

[0018] A third aspect of the present invention provides a sodium-ion battery, comprising a positive electrode material and a negative electrode material, wherein the negative electrode material is the aforementioned starch-coated hard carbon negative electrode material. Detailed Implementation

[0019] This invention provides a sodium-ion battery, comprising a positive electrode material and a negative electrode material. The positive electrode material includes at least one of sodium cobaltate, sodium iron phosphate, sodium nickel cobalt manganese, and sodium nickel cobalt aluminum. The negative electrode material is a starch-coated hard carbon negative electrode material provided by this invention. This starch-coated hard carbon negative electrode material can be used alone or in combination with other negative electrode materials (e.g., expanded graphite, graphite intercalation compounds, and soft carbon). The preparation method of the starch-coated hard carbon negative electrode material of this invention includes the following steps:

[0020] (1) Hard carbon precursor is pre-carbonized, crushed and carbonized in one step to obtain hard carbon powder;

[0021] (2) Mix hard carbon powder and starch evenly to obtain mixed powder, dissolve starch modifier in solvent to form modification solution, react the modification solution with mixed powder and dry to obtain modified precursor;

[0022] (3) The modified precursor is subjected to secondary carbonization and sieving.

[0023] In step (1), the hard carbon precursor is selected from at least one of biomass, coal, and resin. Specifically, the biomass may be selected from at least one of microcrystalline cellulose, wheat straw, and rice husk; the coal may be selected from at least one of lignite, sub-bituminous coal, bituminous coal, and anthracite; and the resin may be selected from phenolic resin. In some technical solutions, the hard carbon precursor is selected from microcrystalline cellulose. In some technical solutions, the hard carbon precursor is selected from rice husk. In some technical solutions, the hard carbon precursor is selected from phenolic resin. In some technical solutions, the hard carbon precursor is selected from bituminous coal.

[0024] Pre-carbonization is carried out in an inert atmosphere, selected from at least one of nitrogen and argon. The pre-carbonization temperature is 400℃ to 700℃, and in some technical solutions, it is 420℃ to 660℃. In some technical solutions, the pre-carbonization temperature is 465℃ to 645℃. As examples, the pre-carbonization temperature can be, but is not limited to, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, 620℃, 640℃, 660℃, 680℃, or 700℃. The pre-carbonization time is 0.5h to 10h, and in some technical solutions, it is 2h to 8h. As an example, the pre-carbonization time can be, but is not limited to, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h. The hard carbon precursor is pre-carbonized at 400℃ to 700℃. At this temperature, microcrystals fully develop and solidify, forming the basic structure of hard carbon.

[0025] The pulverization can be carried out in an air jet mill, and the particle size Dv 50 of the material after air jet milling is 3μm to 8μm. As an example, the particle size Dv 50 of the pulverized material can be, but is not limited to, 3μm, 3.2μm, 3.4μm, 3.5μm, 3.6μm, 3.8μm, 4μm, 4.2μm, 4.4μm, 4.6μm, 4.8μm, 5μm, 5.2μm, 5.4μm, 5.6μm, 5.8μm, 6μm, 7μm, and 8μm. The specific surface area of ​​the pulverized material is 10m². 2 / g~200m 2 / g. As an example, the specific surface area of ​​the pulverized material can be, but is not limited to, 10m². 2 / g, 15m 2 / g、20m 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g、60m 2 / g、80m2 / g, 100m 2 / g, 120m 2 / g, 140m 2 / g、460m 2 / g、180m 2 / g、200m 2 / g. Controlling the particle size and specific surface area of ​​the pulverized material within this range can provide a suitable pore structure for subsequent carbonization.

[0026] The primary carbonization is carried out in an inert atmosphere, selected from at least one of nitrogen and argon. The primary carbonization temperature is 1100℃ to 1600℃, and in some technical solutions, the primary carbonization temperature is 1250℃ to 1460℃. For example, the primary carbonization temperature can be, but is not limited to, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, 1500℃, 1550℃, or 1600℃. The primary carbonization time is 0.5h to 10h, and for example, the primary carbonization time can be, but is not limited to, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h.

[0027] In step (2), the mass ratio of hard charcoal powder to starch is 1:0.05 to 0.5. In some technical solutions, the mass ratio of hard charcoal powder to starch is 1:0.08 to 0.4. As an example, the mass ratio of hard charcoal powder to starch can be, but is not limited to, 1:0.05, 1:0.06, 1:0.08, 1:0.1, 1:0.12, 1:0.14, 1:0.16, 1:0.18, 1:0.2, 1:0.22, 1:0.24, 1:0.26, 1:0.28, 1:0.3, 1:0.35, 1:0.4, 1:0.5. Starch modifiers include amine organic compounds and ester organic compounds. The mass ratio of amine organic compounds, ester organic compounds, and solvent is 0.2 to 0.5:0.5 to 0.8:1.0 to 1.5. In some technical solutions, the mass ratio of amine organic compounds, ester organic compounds, and solvent is 0.3–0.5:0.6–0.8:1.1–1.5; in other technical solutions, the mass ratio is 0.3–0.4:0.6–0.7:1.1–1.4. As an example, the mass ratio of amine organic compounds, ester organic compounds, and solvent can be, but is not limited to, 0.2:0.5:1.0, 0.3:0.5:1.0, 0.4:0.5:1.0, 0.5:0.5:1.0, 0.2:0.6:1.0, 0.3:0.6:1.0, 0.4:0.6:1.0, 0.5:0.6:1.0, 0.2:0.7:1.0, 0.3:0.7:1.0, and 0.4:0.7:1. 0.0, 0.5:0.7:1.0, 0.2:0.8:1.0, 0.3:0.8:1.0, 0.4:0.8:1.0, 0.5:0.8:1.0, 0.2:0.5:1.2, 0.3:0.5:1.2, 0.4:0.5:1.2, 0.5:0.5:1.2, 0.2:0.5:1.5, 0.3:0.5:1.5, 0.4:0.5:1.5, 0.5:0.5:1.5. The starch is selected from at least one of wheat starch, corn starch, and potato starch. The amine organic compound is selected from at least one of acrylamide, ethylenediamine, and aniline; the ester organic compound is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate, and dicyclohexylmethane diisocyanate; and the solvent is selected from at least one of petroleum ether, ethyl acetate, acetone, and tetrahydrofuran. Amine and ester organic compounds are used as starch modifiers. Amine organic compounds can be grafted onto starch to improve its swelling properties, making the starch coating on the hard carbon surface more uniform. At the same time, the grafted nitrogen-containing functional groups increase the content of pyridine and pyrrole nitrogen formed after carbonization, which can provide more electron transport channels and more active sites, thereby increasing the conductivity and topological defects of the starch-coated hard carbon anode material. In addition, the incorporation of nitrogen-containing functional groups can change the atomic structure of the graphite carbon edge or bulk phase, thereby improving the battery rate performance and cycle performance.The ester organic compounds of the present invention are specifically isocyanate organic compounds, whose isocyanate groups can react with the hydroxyl groups in starch to form a cross-linked structure, which can increase the adhesion between starch and the hard carbon backbone, provide more closed-cell structures, reduce the specific surface area of ​​hard carbon, and improve the first coulombic efficiency and specific capacity.

[0028] The mass ratio of the modified solution to the mixed powder is 0.5 to 2:1. As examples, the mass ratio of the modified solution to the mixed powder can be, but is not limited to, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, or 2:1. The reaction temperature is 50℃ to 100℃. As examples, the reaction temperature can be, but is not limited to, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, or 100℃. The reaction time is 1 hour to 10 hours. As examples, the reaction time can be, but is not limited to, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 9 hours, or 10 hours. Drying can be carried out in an oven at a temperature of 80℃ to 250℃. In some technical solutions, the drying temperature is 85℃ to 240℃, and in others, it is 90℃ to 188℃. For example, the drying temperature can be, but is not limited to, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 200℃, or 250℃. The drying time is greater than 5 hours.

[0029] In step (3), the secondary carbonization is carried out in an inert atmosphere, which is selected from at least one of nitrogen and argon. The temperature of the secondary carbonization is 900℃ to 1400℃. For example, the temperature of the secondary carbonization can be, but is not limited to, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃, and 1400℃. The holding time of the secondary carbonization is 0.5h to 10h. For example, the holding time can be, but is not limited to, 0.5h, 1h, 2h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 7h, 8h, 9h, and 10h. After secondary carbonization, the material is first dispersed in a mixer and then screened. The screen mesh used for screening is 200 to 400 mesh. For example, the screen mesh used for screening can be, but is not limited to, 200, 220, 240, 260, 280, 300, 325, 335, 345, 350, 360, 370, 380, 390, or 400 mesh.

[0030] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0031] Example 1

[0032] This embodiment describes a method for preparing a starch-coated hard carbon anode material, including the following steps:

[0033] (1) Under a nitrogen atmosphere, 40 kg of microcrystalline cellulose was placed in a box furnace and kept at 500℃ for 2 hours. After the box furnace cooled to room temperature, the material was removed and then pulverized in an air jet mill until the particle size Dv 50 was 5 μm and the specific surface area was 28.5 m². 2 / g, and finally the material is put into the roller kiln and held at 1200℃ for 3 hours under nitrogen atmosphere to obtain hard carbon powder;

[0034] (2) Mix 5 kg of hard carbon powder and 1 kg of corn starch evenly to obtain a mixed powder. Dissolve 0.5 kg of toluene diisocyanate and 0.2 kg of acrylamide in 10 kg of acetone to form a modification solution. Then slowly add the modification solution to the mixed powder and reflux at 50°C for 8 hours. After the reaction is completed, place the product in an oven at 85°C to dry to obtain the modified precursor.

[0035] (3) Under a nitrogen atmosphere, the modified precursor was placed in a roller kiln and kept at 1200℃ for 5 hours. After cooling to room temperature, the material was put into a mixer to disperse it and then screened with a 325 mesh screen to obtain starch-coated hard carbon anode material.

[0036] Example 2

[0037] This embodiment describes a method for preparing a starch-coated hard carbon anode material, including the following steps:

[0038] (1) Under a nitrogen atmosphere, 40 kg of rice husks were placed in a box furnace and kept at 600℃ for 4 hours. After the box furnace cooled to room temperature, the material was removed and then pulverized in an air jet mill until the particle size Dv 50 was 5 μm and the specific surface area was 26.4 m². 2 / g, and finally the material is put into the roller kiln and held at 1300℃ for 3h under nitrogen atmosphere to obtain hard carbon powder;

[0039] (2) Mix 5 kg of hard carbon powder with 0.7 kg of wheat starch to obtain a mixed powder. Dissolve 1 kg of dicyclohexylmethane diisocyanate and 0.3 kg of acrylamide in 2.5 kg of petroleum ether to form a modification solution. Then slowly add the modification solution to the mixed powder and reflux at 90 °C for 6 h. After the reaction is completed, place the product in an oven at 85 °C to dry to obtain the modified precursor.

[0040] (3) Under a nitrogen atmosphere, the modified precursor was placed in a roller kiln and kept at 900°C for 4 hours. After cooling to room temperature, the material was placed in a mixer to disperse it and then screened with a 325-mesh sieve to obtain starch-coated hard carbon anode material.

[0041] Example 3

[0042] This embodiment describes a method for preparing a starch-coated hard carbon anode material, including the following steps:

[0043] (1) Under a nitrogen atmosphere, 40 kg of phenolic resin was placed in a box furnace and kept at 600℃ for 3 hours. After the box furnace cooled to room temperature, the material was removed and then pulverized in an air jet mill until the particle size Dv 50 was 6 μm and the specific surface area was 38.6 m². 2 / g, and finally the material is put into the roller kiln and held at 1400℃ for 4 hours under nitrogen atmosphere to obtain hard carbon powder;

[0044] (2) Mix 5 kg of hard carbon powder with 0.5 kg of potato starch to obtain a mixed powder. Dissolve 1 kg of diphenylmethane diisocyanate and 0.5 kg of ethylenediamine in 5 kg of ethyl acetate to form a modification solution. Then slowly add the modification solution to the mixed powder and reflux at 85 °C for 7 h. After the reaction is complete, place the product in an oven at 85 °C to dry to obtain the modified precursor.

[0045] (3) Under a nitrogen atmosphere, the modified precursor was placed in a roller kiln and kept at 1100℃ for 3 hours. After cooling to room temperature, the material was put into a mixer to disperse it and then screened with a 325 mesh screen to obtain starch-coated hard carbon anode material.

[0046] Example 4

[0047] This embodiment describes a method for preparing a starch-coated hard carbon anode material, including the following steps:

[0048] (1) Under a nitrogen atmosphere, 40 kg of microcrystalline cellulose was placed in a box furnace and kept at 600℃ for 4 hours. After the box furnace cooled to room temperature, the material was removed and then pulverized in an air jet mill until the particle size Dv 50 was 5 μm and the specific surface area was 34.3 m². 2 / g, and finally the material is put into the roller kiln and held at 1400℃ for 5h under nitrogen atmosphere to obtain hard carbon powder;

[0049] (2) Mix 5 kg of hard carbon powder with 0.6 kg of corn starch to obtain a mixed powder. Dissolve 1 kg of diphenylmethane diisocyanate and 0.2 kg of aniline in 5 kg of tetrahydrofuran to form a modification solution. Then slowly add the modification solution to the mixed powder and reflux at 70 °C for 6 h. After the reaction is completed, place the product in an oven at 85 °C to dry to obtain the modified precursor.

[0050] (3) Under a nitrogen atmosphere, the modified precursor was placed in a roller kiln and kept at 1100℃ for 6 hours. After cooling to room temperature, the material was put into a mixer to disperse it and then screened with a 325 mesh screen to obtain starch-coated hard carbon anode material.

[0051] Example 5

[0052] This embodiment describes a method for preparing a starch-coated hard carbon anode material, including the following steps:

[0053] (1) Under a nitrogen atmosphere, 40 kg of bituminous coal was placed in a box furnace and kept at 600℃ for 2 hours. After the box furnace cooled to room temperature, the material was removed and then pulverized in an air jet mill until the particle size Dv 50 was 5 μm and the specific surface area was 10.8 m². 2 / g, and finally the material is put into the roller kiln and held at 1500℃ for 5h under nitrogen atmosphere to obtain hard carbon powder.

[0054] (2) Mix 5 kg of hard carbon powder with 0.5 kg of wheat starch to obtain a mixed powder. Dissolve 1 kg of toluene diisocyanate and 0.4 kg of ethylenediamine in 2.5 kg of ethyl acetate to form a modification solution. Then slowly add the modification solution to the mixed powder and reflux at 80 °C for 8 h. After the reaction is complete, place the product in an oven at 85 °C to dry to obtain the modified precursor.

[0055] (3) Under a nitrogen atmosphere, the modified precursor was placed in a roller kiln and kept at 1000℃ for 5 hours. After cooling to room temperature, the material was put into a mixer to disperse it and then screened with a 325 mesh screen to obtain starch-coated hard carbon anode material.

[0056] Example 6

[0057] This embodiment describes a method for preparing a starch-coated hard carbon anode material, including the following steps:

[0058] (1) Under a nitrogen atmosphere, 40 kg of microcrystalline cellulose was placed in a box furnace and kept at 570℃ for 6 hours. After the box furnace cooled to room temperature, the material was removed and then pulverized in an air jet mill until the particle size Dv 50 was 5 μm and the specific surface area was 18.7 m². 2 / g, and finally the material is put into the roller kiln and held at 1300℃ for 5h under nitrogen atmosphere to obtain hard carbon powder;

[0059] (2) Mix 5 kg of hard carbon powder with 0.25 kg of corn starch to obtain a mixed powder. Dissolve 0.5 kg of diphenylmethane diisocyanate and 0.15 kg of aniline in 2.5 kg of acetone to form a modification solution. Slowly add the modification solution to the mixed powder and reflux at 80 °C for 8 h. After the reaction is complete, dry the product in an oven at 85 °C to obtain the modified precursor.

[0060] (3) Under a nitrogen atmosphere, the modified precursor was placed in a roller kiln and kept at 1200℃ for 6 hours. After cooling to room temperature, the material was put into a mixer to disperse it and then screened with a 325 mesh screen to obtain starch-coated hard carbon anode material.

[0061] Comparative Example 1

[0062] This comparative example illustrates a method for preparing a starch-coated hard carbon anode material, including the following steps:

[0063] (1) Under a nitrogen atmosphere, 40 kg of microcrystalline cellulose was placed in a box furnace and kept at 500℃ for 2 hours. After the box furnace cooled to room temperature, the material was removed and then pulverized in an air jet mill until the particle size Dv 50 was 5 μm and the specific surface area was 31.8 m². 2 / g, and finally the material is put into the roller kiln and held at 1200℃ for 3 hours under nitrogen atmosphere to obtain hard carbon powder;

[0064] (2) Mix 5 kg of hard carbon powder and 1 kg of corn starch evenly to obtain a mixed powder. Add 10.7 kg of acetone to the mixed powder and reflux at 50 °C for 8 h. After the reaction is complete, place the product in an oven at 85 °C to dry to obtain the modified precursor.

[0065] (3) Under a nitrogen atmosphere, the modified precursor was placed in a roller kiln and kept at 1200℃ for 5 hours. After cooling to room temperature, the material was put into a mixer to disperse it and then screened with a 325 mesh screen to obtain starch-coated hard carbon anode material.

[0066] Comparative Example 2

[0067] This comparative example illustrates a method for preparing a starch-coated hard carbon anode material, including the following steps:

[0068] (1) Under a nitrogen atmosphere, 40 kg of microcrystalline cellulose was placed in a box furnace and kept at 500℃ for 2 hours. After the box furnace cooled to room temperature, the material was removed and then pulverized in an air jet mill until the particle size Dv 50 was 5 μm and the specific surface area was 29.2 m². 2 / g, and finally the material is put into the roller kiln and held at 1200℃ for 3 hours under nitrogen atmosphere to obtain hard carbon powder;

[0069] (2) Mix 5 kg of hard carbon powder with 1 kg of corn starch to obtain a mixed powder. Dissolve 0.7 kg of toluene diisocyanate in 10 kg of acetone to form a modified solution. Then slowly add the modified solution to the mixed powder and reflux at 50 °C for 8 h. After the reaction is complete, place the product in an oven at 85 °C to dry and obtain the modified precursor.

[0070] (3) Under a nitrogen atmosphere, the modified precursor was placed in a roller kiln and kept at 1200℃ for 5 hours. After cooling to room temperature, the material was put into a mixer to disperse it and then screened with a 325 mesh screen to obtain starch-coated hard carbon anode material.

[0071] Comparative Example 3

[0072] This comparative example illustrates a method for preparing a starch-coated hard carbon anode material, including the following steps:

[0073] (1) Under a nitrogen atmosphere, 40 kg of microcrystalline cellulose was placed in a box furnace and kept at 500℃ for 2 hours. After the box furnace cooled to room temperature, the material was removed and then pulverized in an air jet mill until the particle size Dv 50 was 5 μm and the specific surface area was 31.0 m². 2 / g, and finally the material is put into the roller kiln and held at 1200℃ for 3 hours under nitrogen atmosphere to obtain hard carbon powder;

[0074] (2) Mix 5 kg of hard carbon powder and 1 kg of corn starch evenly to obtain mixed powder. Dissolve 0.7 kg of acrylamide in 10 kg of acetone to form a modified solution. Then slowly add the modified solution to the mixed powder and reflux at 50 °C for 8 h. After the reaction is complete, place the product in an oven at 85 °C to dry to obtain the modified precursor.

[0075] (3) Under a nitrogen atmosphere, the modified precursor was placed in a roller kiln and kept at 1200℃ for 5 hours. After cooling to room temperature, the material was put into a mixer to disperse it and then screened with a 325 mesh screen to obtain starch-coated hard carbon anode material.

[0076] The physicochemical properties of the hard carbon powder obtained by primary carbonization in Examples 1-6 and Comparative Examples 1-3, and the starch-coated hard carbon anode material obtained by secondary carbonization were tested. They were then used to prepare half-cells for electrochemical performance testing. The preparation process and test conditions of the half-cells are as follows, and the test results are shown in Table 1.

[0077] Specific surface area: The nitrogen adsorption / desorption isotherms of the material were obtained by a Micromeritics ASAP 2460 analyzer, and its specific surface area was calculated by the BET method.

[0078] Closed-pore volume: calculated by CO2 adsorption-desorption pore size analysis and DFT density functional theory.

[0079] Preparation of half-cells: The hard carbon powder and starch-coated hard carbon negative electrode material from Examples 1-6 and Comparative Examples 1-3 of this invention were used as active materials and uniformly dispersed with carboxymethyl cellulose (CMC) binder in deionized water at a mass ratio of 95:5 to obtain a slurry. This slurry was then coated onto copper foil and dried in a vacuum oven at 120°C for 12 hours. The slurry was then cut into discs with a diameter of 1 cm, and the areal density of the active material loaded on the discs was 0.8–1.0 mg / cm³. 2 In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), using metallic sodium as the counter electrode, and 1 M NaClO4 dissolved in a 1:1 volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) and 5% fluoroethylene carbonate (FEC) as the electrolyte, CR2032 coin cells were assembled. Electrochemical performance tests were conducted on an ILJT332S constant-temperature multichannel battery test cabinet from JEIOTECH (Korea), with a charge / discharge voltage range of 0.005 to 1.5 V. The coin cells prepared above were tested for 0.1C first-cycle capacity, 0.1C first-cycle charge / discharge efficiency, 1C rate capacity ratio, and capacity retention after 300 cycles at 0.5C.

[0080] Table 1. Test results of the coal-based starch-coated hard carbon anode materials prepared in Examples 1-6 and Comparative Examples 1-3.

[0081]

[0082]

[0083]

[0084] The test results are shown in Table 1. As can be seen from the test results of Examples 1-6 and Comparative Examples 1-3, the starch-coated hard carbon anode material prepared by the preparation method of the present invention has better electrochemical performance.

[0085] Further, referring to the test results of Examples 1-6, a comparison of the physicochemical properties of the hard carbon powder obtained by primary carbonization and the starch-coated hard carbon anode material obtained by secondary carbonization in each example shows that the starch-coated hard carbon anode material obtained after modified starch coating has a reduced specific surface area, a closed-cell structure more conducive to sodium storage, and superior initial coulombic efficiency, specific capacity, rate performance, and cycle performance. Specifically, the initial reversible specific capacity at 0.1C is increased by 10 mAh / g to 65 mAh / g, the initial coulombic efficiency is ≥90.1%, the rate capacity ratio at 1C current is increased by 16.9% to 24.1%, and the capacity retention rate after 300 cycles at 0.5C is ≥98.8%.

[0086] Furthermore, a comparison between Example 1 and Comparative Examples 1-3 shows that when only unmodified starch is used to coat the hard carbon powder, or when the starch modifier lacks at least one of amine organic compounds and ester organic compounds, the improvement in the physicochemical properties of the obtained starch-coated hard carbon anode material is relatively limited.

[0087] In summary, this invention uses hard carbon material as the main body and modifies starch in situ through a starch modifier. This allows for uniform adhesion of starch to the hard carbon surface, improving the closed-cell structure and uniform distribution of the starch-coated hard carbon anode material after carbonization, thereby enhancing the initial coulombic efficiency and specific capacity. The starch modifier of this invention includes amine organic compounds and ester organic compounds. The amine organic compounds can be grafted onto starch to enhance its swelling properties, resulting in more uniform starch coating on the hard carbon surface. Simultaneously, the grafted nitrogen-containing functional groups increase the content of pyridine and pyrrole nitrogen formed after carbonization, providing more electron transport channels and active sites, thus increasing the conductivity and topological defects of the starch-coated hard carbon anode material. Furthermore, the incorporation of nitrogen-containing functional groups can alter the atomic structure of the graphite carbon edge or bulk phase, thereby improving the battery's rate performance and cycle performance. The introduction of ester organic compounds can form a binder with starch, increasing the adhesion between starch and the hard carbon backbone, providing more closed-cell structures, reducing the specific surface area of ​​the hard carbon, and improving the initial coulombic efficiency and specific capacity.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing starch-coated hard carbon anode material, characterized in that, Including the following steps: (1) Hard carbon precursor is pre-carbonized, crushed and carbonized in one step to obtain hard carbon powder; (2) The hard carbon powder is mixed with starch to obtain a mixed powder. The starch modifier is dissolved in a solvent to form a modified solution. The modified solution is then reacted with the mixed powder and dried to obtain a modified precursor. The starch modifier includes amine organic compounds and ester organic compounds. The ester organic compounds are selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate and dicyclohexylmethane diisocyanate. The reaction temperature is 50 ℃~100 ℃ and the reaction time is 1 h~10 h. (3) The modified precursor is subjected to secondary carbonization and sieving.

2. The method for preparing starch-coated hard carbon anode material according to claim 1, characterized in that, The hard carbon precursor is selected from at least one of biomass, coal, and resin. The pulverization is carried out in an air jet mill, and the particle size Dv 50 of the pulverized material is 3 μm to 8 μm, with a specific surface area of ​​10 m². 2 / g~200 m 2 / g.

3. The method for preparing starch-coated hard carbon anode material according to claim 1, characterized in that, The pre-carbonization temperature is 400 ℃~700 ℃, the pre-carbonization time is 0.5 h~10 h, the primary carbonization temperature is 1100 ℃~1600 ℃, and the primary carbonization holding time is 0.5 h~10 h.

4. The method for preparing starch-coated hard carbon anode material according to claim 1, characterized in that, The pre-carbonization, primary carbonization, and secondary carbonization are all carried out in an inert atmosphere, each of which is independently selected from at least one of nitrogen and argon.

5. The method for preparing starch-coated hard carbon anode material according to claim 1, characterized in that, The mass ratio of the hard carbon powder to the starch is 1:0.05~0.5, the mass ratio of the amine organic compound, the ester organic compound and the solvent is 0.2~0.5:0.5~0.8:1.0~1.5, and the mass ratio of the modified solution to the mixed powder is 0.5~2:

1.

6. The method for preparing starch-coated hard carbon anode material according to claim 1, characterized in that, The starch is selected from at least one of wheat starch, corn starch and potato starch, the amine organic compound is selected from at least one of acrylamide, ethylenediamine and aniline, and the solvent is selected from at least one of petroleum ether, ethyl acetate, acetone and tetrahydrofuran.

7. The method for preparing starch-coated hard carbon anode material according to claim 1, characterized in that, The drying temperature is 80 ℃ to 250 ℃, and the drying time is greater than 5 h.

8. The method for preparing starch-coated hard carbon anode material according to claim 1, characterized in that, The secondary carbonization temperature is 900 ℃~1400 ℃, the secondary carbonization holding time is 0.5 h~10 h, and the sieving mesh size is 200 mesh~400 mesh.

9. A starch-coated hard carbon anode material, characterized in that, It was prepared using the method described in any one of claims 1 to 8 for preparing starch-coated hard carbon anode material.

10. A sodium-ion battery, comprising a positive electrode material and a negative electrode material, characterized in that, The negative electrode material is the starch-coated hard carbon negative electrode material as described in claim 9.

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