A high-capacity, high-initial-efficiency biomass-based hard carbon composite negative electrode material, a preparation method therefor, and use thereof

Abstract

The application provides a biomass-based hard carbon composite negative electrode material with high capacity and high initial efficiency, and a preparation method and application thereof. The biomass-based hard carbon composite negative electrode material has high capacity and high initial efficiency, and also has excellent cycle performance. AlCl3 and SnCl4 are added into molten pitch, and AlCl3 and SnCl4 react with water in the pitch to generate nano Al2O3 particles and nano SnO2 particles, thereby obtaining modified pitch. After the modified pitch is prepared into a solution, the modified pitch can be filled into pores of a hard carbon precursor and form a coating layer on a surface of the hard carbon precursor in the process of impregnation of the hard carbon precursor. In a high-temperature carbonization process, the hard carbon precursor is converted into hard carbon, nano SnO2 is reduced into nano Sn particles by carbon, and pitch is converted into amorphous carbon. The nano Sn particles, the amorphous carbon and the nano Al2O3 particles are uniformly distributed in pores and on a surface of the hard carbon, and synchronous modification of the inside and the surface of the hard carbon is realized.

Description

Technical Field

[0001] This invention belongs to the technical field of anode materials for sodium-ion batteries, specifically relating to a high-capacity, high-efficiency biomass-based hard carbon composite anode material, its preparation method, and its applications. Background Technology

[0002] With the rapid development of the electric vehicle market, the demand for lithium-ion batteries has surged. However, the reserves of lithium resources in the Earth's crust are limited, resulting in high costs for lithium-ion batteries. Meanwhile, sodium-ion batteries operate on a similar principle to lithium-ion batteries, have near-zero energy density, and are abundant, evenly distributed, and inexpensive, making them a promising candidate for large-scale energy storage devices.

[0003] Hard carbon is the most commonly used anode material in commercial sodium-ion batteries. Currently, there are two main categories of raw materials for hard carbon preparation: petroleum-based and biomass-based. Petroleum-based materials are widely available, and the resulting hard carbon exhibits stable performance and high carbon yield, but its structural characteristics result in lower capacity compared to other materials. Biomass, as a carbon source, is the preferred raw material for hard carbon preparation due to its environmental friendliness and low cost. However, the low initial coulombic efficiency and capacity of currently developed hard carbon anode materials severely restrict the development of sodium-ion batteries. Therefore, there is an urgent need to develop a hard carbon anode material with high capacity and high initial coulombic efficiency. Summary of the Invention

[0004] To address the issues of low initial coulombic efficiency and capacity in existing biomass-based hard carbon anode materials, this invention provides a high-capacity, high-initial-efficiency biomass-based hard carbon composite anode material, its preparation method, and its applications. The biomass-based hard carbon composite anode material exhibits high capacity and initial coulombic efficiency, along with excellent cycling performance.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing a biomass-based hard carbon composite anode material, the method comprising the following steps:

[0007] (1) Biomass was pre-carbonized under a nitrogen atmosphere to prepare pre-carbonized products;

[0008] (2) The pre-carbonized product from step (1) is mixed with an acid solution, impregnated, filtered, and washed with water until neutral to obtain a hard carbon precursor.

[0009] (3) Place the asphalt in a reaction vessel and heat it to 120-160℃. Add AlCl3 and SnCl4 under stirring conditions and react for 0.5-1 hours to obtain modified asphalt.

[0010] (4) Mix the modified asphalt from step (3) with an organic solvent to obtain a modified asphalt solution;

[0011] (5) Place the hard carbon precursor from step (2) into the reactor, evacuate the reactor, add the modified asphalt solution from step (4), stir the mixture at the same time, pressurize and impregnate, after the pressurization and impregnation is completed, reduce the pressure to make the pressure inside and outside the reactor the same, introduce nitrogen gas, heat to remove organic solvent, and obtain the impregnated hard carbon precursor.

[0012] (6) The impregnated hard carbon precursor from step (5) is placed in a high-temperature furnace and carbonized under a nitrogen atmosphere to prepare the biomass-based hard carbon composite anode material.

[0013] According to an embodiment of the present invention, in step (1), the source of the biomass is not specifically defined, and may be at least one of lychee wood, apple wood, poplar wood, bamboo, fruit shell, straw, coconut shell and corn cob.

[0014] According to an embodiment of the present invention, in step (1), it is preferable to clean the biomass raw material, then dry it at 60-120°C, and then perform preliminary crushing.

[0015] According to an embodiment of the present invention, in step (1), the temperature of the pre-carbonization treatment is 300℃-600℃, for example, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, or 600℃; the time of the pre-carbonization treatment is 1-6 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours. The pre-carbonization treatment can remove organic matter from biomass and obtain a pre-carbonized product containing pores.

[0016] According to an embodiment of the present invention, in step (1), after the pre-carbonization treatment is completed, the pre-carbonization product is preferably cooled to room temperature in the furnace.

[0017] According to an embodiment of the present invention, in step (1), it is preferable to pulverize the product after pre-carbonization treatment to obtain a pre-carbonized product with a median particle size of 5-8 μm.

[0018] According to an embodiment of the present invention, in step (2), the pH value of the acid solution is 3-4.

[0019] According to an embodiment of the present invention, in step (2), the acid solution can be at least one of hydrochloric acid aqueous solution, sulfuric acid aqueous solution, nitric acid aqueous solution, and hydrofluoric acid aqueous solution.

[0020] According to an embodiment of the present invention, in step (2), the soaking time is 12-24 hours, for example, 12 hours, 16 hours, 18 hours or 24 hours.

[0021] According to an embodiment of the present invention, in step (2), the impregnation is atmospheric pressure impregnation.

[0022] According to an embodiment of the present invention, in step (2), the pre-carbonized product from step (1) and the acid solution are mixed under stirring conditions, and then the pre-carbonized product is completely immersed in the acid solution, that is, the acid solution completely covers the pre-carbonized product.

[0023] According to an embodiment of the present invention, in step (2), after impregnation, the acid solution is removed by filtration, and then the solid component is washed with deionized water until neutral.

[0024] According to an embodiment of the present invention, in step (3), the softening point of the asphalt is 65-75°C, for example, 65°C, 70°C or 75°C.

[0025] According to an embodiment of the present invention, in step (3), the water content in the asphalt is 2-3 wt%, for example, 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt%, or 3 wt%.

[0026] According to an embodiment of the present invention, in step (3), asphalt is placed in a reaction vessel and heated to 120°C, 130°C, 140°C, 150°C, or 160°C, and reacted at this temperature for 0.5-1 hour. During the reaction, the AlCl3 and SnCl4 react with water in the asphalt to generate nano-Al2O3 and nano-SnO2 particles, and the generated nano-Al2O3 and nano-SnO2 particles are uniformly distributed in the asphalt, thus preparing the modified asphalt. Compared to methods that directly add nano-Al2O3 and nano-SnO2 particles to asphalt to obtain modified asphalt, the in-situ synthesis method of nano-Al2O3 and nano-SnO2 particles of this invention allows for the uniform distribution of nano-Al2O3 and nano-SnO2 particles in the asphalt. During the subsequent carbonization process, the nano-SnO2 is reduced to metallic Sn and uniformly distributed in the amorphous carbon after asphalt carbonization. The amorphous carbon exists in the pores and surface of the hard carbon, which is beneficial for improving the capacity of the hard carbon composite anode material. Simultaneously, the in-situ synthesis method of nano-sized Al2O3 and nano-SnO2 particles of this invention avoids the situation where uneven dispersion of metal oxides (such as agglomeration) prevents the modified asphalt from penetrating the pre-carbonized product during impregnation, thus hindering the effective improvement of the initial coulombic efficiency and capacity of the anode material. Furthermore, conducting the reaction at this temperature can also increase the softening point of the asphalt (from 65-75℃ to 75-95℃).

[0027] According to an embodiment of the present invention, in step (3), the softening point of the modified asphalt is 75-95℃, for example, 75℃, 80℃, 85℃, 90℃ or 95℃.

[0028] According to an embodiment of the present invention, in step (3), the mass ratio of AlCl3 to asphalt is (0.5-3):100, for example, 0.5:100, 0.6:100, 0.8:100, 1.0:100, 1.2:100, 1.5:100, 1.8:100, 2:100, 2.2:100, 2.5:100, 2.8:100 or 3:100.

[0029] According to an embodiment of the present invention, in step (3), the mass ratio of SnCl4 to asphalt is (2-12):100, for example, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, 11:100 or 12:100.

[0030] According to an embodiment of the present invention, in step (4), the organic solvent is selected from hydrocarbon organic solvents, such as any one or a mixture of two of wash oil, naphthalene oil, and phenol oil.

[0031] According to an embodiment of the present invention, in step (4), the mass ratio of the modified asphalt to the organic solvent is 1:(1-1.5), for example, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4 or 1:1.5.

[0032] According to an embodiment of the present invention, in step (4), the mixing is carried out under stirring conditions, and the stirring can make the modified asphalt fully dissolve in the organic solvent to form a modified asphalt solution.

[0033] According to an embodiment of the present invention, in step (5), the mass ratio of the modified asphalt solution to the hard carbon precursor in step (2) is (40-60):1, for example, 40:1, 45:1, 50:1, 55:1 or 60:1.

[0034] According to an embodiment of the present invention, in step (5), the stirring speed is 500-800 r / min.

[0035] According to an embodiment of the present invention, in step (5), the method of adding the modified asphalt solution in step (4) is, for example, to open the modified asphalt solution suction valve, suck the modified asphalt solution in step (4) into the reaction vessel, and close the suction valve after the liquid injection is completed, and stop the vacuuming.

[0036] According to an embodiment of the present invention, in step (5), the vacuum degree of the reactor is 0.07-0.09 MPa.

[0037] According to an embodiment of the present invention, in step (5), the pressure of the pressure impregnation is 1MPa-3MPa, for example 1MPa, 1.5MPa, 2MPa, 2.5MPa, or 3MPa; and the pressure impregnation time is 1-5 hours, for example 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours.

[0038] According to an embodiment of the present invention, in step (5), the heating temperature is 200-300°C; the heating time is not specifically defined, and can be carried out until the organic solvent is completely removed.

[0039] According to an embodiment of the present invention, in step (6), the temperature of the carbonization treatment is 900℃-1200℃, for example, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃ or 1200℃; the time of the carbonization treatment is 1-6 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0040] According to an embodiment of the present invention, in step (6), it is preferable to disintegrate the carbonized product to obtain a biomass-based hard carbon composite anode material with a median particle size of 5-8 μm.

[0041] The present invention also provides a biomass-based hard carbon composite anode material prepared by the above method.

[0042] According to an embodiment of the present invention, the biomass-based hard carbon composite anode material has a core-shell structure, wherein the core comprises hard carbon, nano-Sn particles, amorphous carbon, and nano-Al2O3 particles; the nano-Sn particles, amorphous carbon, and nano-Al2O3 particles are distributed in the pores of the hard carbon; and the shell is a composite of nano-Sn particles, nano-Al2O3 particles, and amorphous carbon.

[0043] According to an embodiment of the present invention, the median particle size of the nano Sn particles is 25-35 nm, for example, 30 nm.

[0044] According to an embodiment of the present invention, the median particle size of the nano-Al2O3 particles is 30-45 nm, for example, 35 nm or 40 nm.

[0045] According to an embodiment of the present invention, the median particle size of the biomass-based hard carbon composite anode material is 5-8 μm.

[0046] According to an embodiment of the present invention, the thickness of the shell is 80-120 nm.

[0047] The present invention also provides the use of the above-mentioned biomass-based hard carbon composite anode material for sodium-ion batteries, preferably for the preparation of anodes for sodium-ion batteries.

[0048] The present invention also provides a negative electrode for sodium-ion batteries, the negative electrode comprising the above-mentioned biomass-based hard carbon composite negative electrode material.

[0049] The present invention also provides a sodium-ion battery, wherein the sodium-ion battery comprises the above-mentioned biomass-based hard carbon composite negative electrode material.

[0050] The beneficial effects of this invention are:

[0051] This invention involves pre-carbonizing and acid washing biomass sequentially, while simultaneously adding AlCl3 and SnCl4 to molten asphalt. AlCl3 and SnCl4 react with water in the asphalt to generate nano-Al2O3 particles and nano-SnO2 particles, resulting in modified asphalt. The nano-Al2O3 and nano-SnO2 particles are uniformly dispersed in the modified asphalt. When the modified asphalt is prepared into a solution and impregnated with a hard carbon precursor, it fills the pores of the hard carbon precursor and forms a coating layer on its surface. During high-temperature carbonization, the hard carbon precursor transforms into hard carbon, the nano-SnO2 is reduced to nano-Sn particles, and the asphalt transforms into amorphous carbon. The nano-Sn particles, amorphous carbon, and nano-Al2O3 particles are uniformly distributed in the pores and on the surface of the hard carbon, achieving simultaneous modification of the hard carbon's interior and exterior surfaces. In addition, nano-Al2O3 particles and amorphous carbon can enhance the structural integrity and strength of hard carbon composite anode materials, and can also effectively inhibit the decomposition of electrolyte on the surface of hard carbon composite anode materials, thereby effectively improving the stability of the electrode interface and enhancing the cycle stability and first coulombic efficiency of sodium-ion batteries. Nano-Sn particles can improve the capacity of hard carbon composite anode materials, resulting in the prepared hard carbon composite anode materials exhibiting high first coulombic efficiency, high capacity and excellent cycle performance. Detailed Implementation

[0052] The preparation method of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0053] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0054] Example 1

[0055] (1) Carbonize the coconut shell at 400°C for 4 hours under a nitrogen atmosphere, cool it to room temperature, and then crush it to obtain material 1;

[0056] (2) Soak material 1 from step (1) in hydrochloric acid solution with pH 3 for 15 hours, filter, wash with deionized water until neutral, and dry to obtain material 2.

[0057] (3) Place 100g of asphalt (softening point 68℃) into a reaction vessel and heat it to 120℃. Under stirring conditions (500r / min), add 1g of AlCl3 and 6g of SnCl4 to the molten asphalt and react for 0.5 hours to obtain modified asphalt (softening point 78℃).

[0058] (4) Mix 100g of modified asphalt and 100g of wash oil from step (3) and stir to fully dissolve the asphalt to obtain a modified asphalt solution.

[0059] (5) Put 4g of material 2 into the reactor and vacuum it for 60min. When the vacuum degree of the reactor reaches 0.07MPa, open the modified asphalt solution suction valve and suck all 200g of the modified asphalt solution obtained in step (4) into the reactor. After the liquid is fed in, close the suction valve and stop vacuuming. At the same time, stir the mixture (20r / min) for 40min and then soak it at 1.5MPa for 3 hours. After soaking, reduce the pressure to make the pressure inside and outside the reactor the same, then introduce nitrogen and heat it to 230℃ to remove the washing oil and obtain material 3.

[0060] (6) Place the material 3 from step (5) in a high-temperature furnace and carbonize it at 1200°C for 4 hours under a nitrogen atmosphere. After cooling to room temperature, pulverize it to obtain a biomass-based hard carbon composite anode material.

[0061] The biomass-based hard carbon composite anode material has a core-shell structure. The core includes hard carbon, nano-Sn particles, amorphous carbon, and nano-Al2O3 particles. The nano-Sn particles, amorphous carbon, and nano-Al2O3 particles are distributed in the pores of the hard carbon. The shell is a composite of nano-Sn particles, nano-Al2O3 particles, and amorphous carbon.

[0062] Example 2

[0063] (1) Carbonize the fruit shell at 500°C for 2 hours under nitrogen atmosphere, cool it to room temperature, and then crush it to obtain material 1;

[0064] (2) Soak material 1 from step (1) in a nitric acid solution with pH 4 for 14 hours, filter, wash with deionized water until neutral, and dry to obtain material 2.

[0065] (3) Place 100g of asphalt (softening point 70℃) into a reaction vessel and heat it to 120℃. Under stirring conditions (500r / min), add 1.5g of AlCl3 and 4g of SnCl4 to the molten asphalt and react for 0.6 hours to obtain modified asphalt (softening point 85℃).

[0066] (4) Mix 100g of modified asphalt and 120g of naphthalene oil from step (3) and stir to fully dissolve the asphalt to obtain a modified asphalt solution.

[0067] (5) Put 5g of material 2 into the reactor and vacuum for 60min. When the vacuum degree of the reactor reaches 0.07MPa, open the suction valve of the modified asphalt solution and suck all 240g of the modified asphalt solution obtained in step (4) into the reactor. After the liquid is fed in, close the suction valve and stop vacuuming. At the same time, stir the mixture (30r / min) for 30min and then impregnate it under 2MPa conditions. After impregnation, reduce the pressure to make the pressure inside and outside the reactor the same, then introduce nitrogen and heat to 250℃ to remove naphthalene oil and obtain material 3.

[0068] (6) Place the material 3 from step (5) in a high-temperature furnace and carbonize it at 1400°C for 3 hours under a nitrogen atmosphere. After cooling to room temperature, pulverize it to obtain a biomass-based hard carbon composite anode material.

[0069] The biomass-based hard carbon composite anode material has a core-shell structure. The core includes hard carbon, nano-Sn particles, amorphous carbon, and nano-Al2O3 particles. The nano-Sn particles, amorphous carbon, and nano-Al2O3 particles are distributed in the pores of the hard carbon. The shell is a composite of nano-Sn particles, nano-Al2O3 particles, and amorphous carbon.

[0070] Example 3

[0071] (1) Carbonize the coconut shell at 350°C for 6 hours under nitrogen atmosphere, cool it to room temperature, and then crush it to obtain material 1;

[0072] (2) Soak material 1 from step (1) in hydrochloric acid solution with pH 3 for 15 hours, filter, wash with deionized water until neutral, and dry to obtain material 2.

[0073] (3) Place 100g of asphalt (softening point 75℃) into a reaction vessel and heat it to 100℃. Under stirring conditions (650r / min), add 2g of AlCl3 and 7g of SnCl4 to the molten asphalt and react for 0.5 hours to obtain modified asphalt (softening point 95℃).

[0074] (4) Mix 100g of modified asphalt and 150g of phenolic oil from step (3) and stir to fully dissolve the asphalt to obtain a modified asphalt solution.

[0075] (5) Put 5g of material 2 into the reactor and vacuum for 60min. When the vacuum degree of the reactor reaches 0.07MPa, open the modified asphalt solution suction valve and suck all 250g of the modified asphalt solution obtained in step (4) into the reactor. After the liquid is fed in, close the suction valve and stop vacuuming. At the same time, stir the mixture (20r / min) for 40min and then impregnate it under 2.5MPa. After impregnation, reduce the pressure to make the pressure inside and outside the reactor the same, then introduce nitrogen and heat to 280℃ to remove phenol oil and obtain material 3.

[0076] (6) Place the material 3 from step (5) in a high-temperature furnace and carbonize it at 1200°C for 4 hours under a nitrogen atmosphere. After cooling to room temperature, pulverize it to obtain a biomass-based hard carbon composite anode material.

[0077] The biomass-based hard carbon composite anode material has a core-shell structure. The core includes hard carbon, nano-Sn particles, amorphous carbon, and nano-Al2O3 particles. The nano-Sn particles, amorphous carbon, and nano-Al2O3 particles are distributed in the pores of the hard carbon. The shell is a composite of nano-Sn particles, nano-Al2O3 particles, and amorphous carbon.

[0078] Example 4

[0079] (1) Carbonize the coconut shell at 600°C for 2 hours under nitrogen atmosphere, cool it to room temperature, and then crush it to obtain material 1;

[0080] (2) Soak material 1 from step (1) in hydrochloric acid aqueous solution with pH 4 for 20 hours, filter, wash with deionized water until neutral, and dry to obtain material 2.

[0081] (3) Place 100g of asphalt (softening point 72℃) into a reaction vessel and heat it to 120℃. Under stirring conditions (600r / min), add 0.6g of AlCl3 and 6g of SnCl4 to the molten asphalt and react for 0.5 hours to obtain modified asphalt (softening point 80℃).

[0082] (4) Mix 100g of modified asphalt and 100g of wash oil from step (3) and stir to fully dissolve the asphalt to obtain a modified asphalt solution.

[0083] (5) Put 5g of material 2 into the reactor and vacuum for 60min. When the vacuum degree of the reactor reaches 0.07MPa, open the modified asphalt solution suction valve and suck all 200g of the modified asphalt solution obtained in step (4) into the reactor. After the liquid is fed in, close the suction valve and stop vacuuming. At the same time, stir the mixture (25r / min) for 40min and then impregnate it under 1.5MPa. After impregnation, reduce the pressure to make the pressure inside and outside the reactor the same, then introduce nitrogen and heat to 250℃ to remove the washing oil and obtain material 3.

[0084] (6) Place the material 3 from step (5) in a high-temperature furnace and carbonize it at 1200°C for 4 hours under a nitrogen atmosphere. After cooling to room temperature, pulverize it to obtain a biomass-based hard carbon composite anode material.

[0085] The biomass-based hard carbon composite anode material has a core-shell structure. The core includes hard carbon, nano-Sn particles, amorphous carbon, and nano-Al2O3 particles. The nano-Sn particles, amorphous carbon, and nano-Al2O3 particles are distributed in the pores of the hard carbon. The shell is a composite of nano-Sn particles, nano-Al2O3 particles, and amorphous carbon.

[0086] Comparative Example 1

[0087] (1) Carbonize the coconut shell at 400°C for 4 hours under a nitrogen atmosphere, cool it to room temperature, and then crush it to obtain material 1;

[0088] (2) Soak material 1 from step (1) in hydrochloric acid solution with pH 3 for 15 hours, filter, wash with deionized water until neutral, and dry to obtain material 2.

[0089] (3) Place 100g of asphalt (softening point 68℃) into a reaction vessel and heat it to 120℃. Keep it at that temperature for 0.5 hours to obtain modified asphalt.

[0090] (4) Mix 100g of modified asphalt and 100g of wash oil from step (3) and stir to fully dissolve the asphalt to obtain a modified asphalt solution.

[0091] (5) Put 4g of material 2 into the reactor and vacuum it for 60min. When the vacuum degree of the reactor reaches 0.07MPa, open the modified asphalt solution suction valve and suck all 200g of the modified asphalt solution obtained in step (4) into the reactor. After the liquid is fed in, close the suction valve and stop vacuuming. At the same time, stir the mixture (20r / min) for 40min and then soak it at 1.5MPa for 3 hours. After soaking, reduce the pressure to make the pressure inside and outside the reactor the same, then introduce nitrogen and heat it to 230℃ to remove the washing oil and obtain material 3.

[0092] (6) Place the material 3 from step (5) in a high-temperature furnace and carbonize it at 1200°C for 4 hours under a nitrogen atmosphere. After cooling to room temperature, pulverize it to obtain a biomass-based hard carbon composite anode material.

[0093] The biomass-based hard carbon composite anode material has a core-shell structure, with the core comprising hard carbon and amorphous carbon; the amorphous carbon is distributed in the pores of the hard carbon; and the shell is amorphous carbon.

[0094] The biomass-based hard carbon composite anode materials prepared in Examples 1-4 and Comparative Example 1 were used as anode materials for sodium-ion batteries, and their electrochemical performance was tested using the following methods:

[0095] The biomass-based hard carbon composite negative electrode material, conductive agent Super P, binder sodium carboxymethyl cellulose (CMC), and aqueous binder (SBR) prepared above were weighed in a mass ratio of 95:2:1.5:1.5. After being thoroughly ground in an agate mortar, a small amount of deionized water was added to form a uniform black paste. This paste was coated onto a copper foil current collector as a test electrode, and a sodium metal sheet was used as a control electrode to assemble a coin cell. The electrolyte was 1M sodium hexafluorophosphate dissolved in a 1:1 volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed solution. 5 wt.% of fluoroethylene carbonate (FEC) was added to the electrolyte as an additive. Glass fiber was used as the separator, and CR2032 stainless steel was used as the battery casing to assemble the coin cell. The discharge capacity and initial coulombic efficiency were tested at a constant rate of 0.1C within a voltage range of 0.01-3.0V.

[0096] Using the biomass-based hard carbon composite anode material prepared above as the anode, sodium nickel iron manganese oxide as the cathode, and 1M NaPF6+EC:DEC:DMC (volume ratio 1:1:1) solution as the electrolyte, a full cell was assembled in a stacked manner. The cell was tested at room temperature with a 1C rate, and the voltage range was 1.5-3.9V. The cycle performance was then tested.

[0097] Table 1 Electrochemical performance of biomass-based hard carbon composite anode materials

[0098]

[0099] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a biomass-based hard carbon composite anode material, the method comprising the following steps: (1) Biomass was pre-carbonized under a nitrogen atmosphere to prepare pre-carbonized products; (2) The pre-carbonized product from step (1) is mixed with an acid solution, impregnated, filtered, and washed with water until neutral to obtain a hard carbon precursor; (3) Place the asphalt in a reaction vessel and heat it to 120-160℃. Add AlCl3 and SnCl4 under stirring conditions and react for 0.5-1 hours to obtain modified asphalt. (4) Mix the modified asphalt from step (3) with an organic solvent to obtain a modified asphalt solution; (5) Place the hard carbon precursor from step (2) into the reactor, evacuate the reactor, add the modified asphalt solution from step (4), stir the mixture at the same time, pressurize and impregnate, after pressurization and impregnation are completed, reduce the pressure to make the pressure inside and outside the reactor the same, introduce nitrogen gas, heat to remove organic solvent, and obtain the impregnated hard carbon precursor. (6) The impregnated hard carbon precursor from step (5) is placed in a high-temperature furnace and carbonized under a nitrogen atmosphere to prepare the biomass-based hard carbon composite anode material. In step (3), the water content in the asphalt is 2-3 wt%.

2. The preparation method according to claim 1, wherein, In step (1), the biomass is at least one of lychee wood, apple wood, poplar wood, bamboo, fruit shell, straw and corn cob; And / or, in step (1), the temperature of the pre-carbonization treatment is 300℃-600℃, and the time of the pre-carbonization treatment is 1-6 hours; And / or, in step (1), the pre-carbonized product is pulverized to obtain a pre-carbonized product with a median particle size of 5-8 μm; And / or, in step (2), the pH value of the acid solution is 3-4; And / or, in step (2), the acid solution is at least one of hydrochloric acid aqueous solution, sulfuric acid aqueous solution, nitric acid aqueous solution, and hydrofluoric acid aqueous solution.

3. The preparation method according to claim 1, wherein, In step (3), the softening point of the asphalt is 65-75℃; And / or, in step (3), the mass ratio of AlCl3 to asphalt is (0.5-3):100; And / or, in step (3), the mass ratio of SnCl4 to asphalt is (2-12):

100.

4. The preparation method according to claim 1, wherein, In step (4), the organic solvent is selected from any one or a mixture of two of wash oil, naphthalene oil, and phenol oil; And / or, in step (4), the mass ratio of the modified asphalt to the organic solvent is 1:(1-1.5).

5. The preparation method according to any one of claims 1-4, wherein, In step (5), the mass ratio of the modified asphalt solution to the hard carbon precursor in step (2) is (40-60):1; And / or, in step (5), the pressure of the pressure impregnation is 1MPa-3MPa; the pressure impregnation time is 1-5 hours; And / or, in step (5), the heating temperature is 200-300℃.

6. The preparation method according to any one of claims 1-4, wherein, In step (6), the carbonization temperature is 900℃-1200℃; the carbonization time is 1-6 hours.

7. The biomass-based hard carbon composite anode material prepared by the method according to any one of claims 1-6.

8. The biomass-based hard carbon composite anode material according to claim 7, wherein, The biomass-based hard carbon composite anode material has a core-shell structure. The core includes hard carbon, nano-Sn particles, amorphous carbon, and nano-Al2O3 particles. The nano-Sn particles, amorphous carbon, and nano-Al2O3 particles are distributed in the pores of the hard carbon. The shell is a composite of nano-Sn particles, nano-Al2O3 particles, and amorphous carbon. The median particle size of the nano Sn particles is 25-35 nm; the median particle size of the nano Al2O3 particles is 30-45 nm; and the thickness of the shell is 80-120 nm.

9. The biomass-based hard carbon composite anode material according to claim 8, wherein, The median particle size of the biomass-based hard carbon composite anode material is 5-8 μm.

10. A negative electrode for a sodium-ion battery, the negative electrode comprising the biomass-based hard carbon composite negative electrode material according to any one of claims 7-9.

11. A sodium-ion battery, wherein the sodium-ion battery comprises the biomass-based hard carbon composite anode material according to any one of claims 7-9.

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