Biomass-based hard carbon composite material quantitatively prepared based on hard carbon pore volume, preparation method of biomass-based hard carbon composite material, negative electrode material and battery

Abstract

The invention discloses a biomass-based hard carbon composite material quantitatively prepared based on a hard carbon pore volume and a method thereof, a negative electrode material and a battery. The method provided by the invention comprises the following steps: firstly, uniformly dispersing a pore-forming agent in biomass powder, pre-carbonizing, and washing to obtain a porous carbon matrix; according to the steps, pore forming is completed while pre-carbonization is completed, the porous carbon matrix with a certain pore volume is prepared, the dosage of the soft carbon precursor is designed based on the total pore volume in the subsequent steps, quantification and rationalization of the dosage of the soft carbon precursor can be achieved, the obtained product is good in performance consistency, and industrial production can be achieved. And the problem that subsequent soft carbon raw materials cannot be scientifically matched due to diversity of raw materials of biomass with different sources can also be avoided. Besides, by utilizing the chemical cross-linking reaction of asphalt and biomass carbon, not only is the carbon residue rate improved, but also a unique structure rich in closed pores and ultra-micropores is constructed, and the problems of low initial coulombic efficiency and insufficient platform capacity of traditional hard carbon are effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, and particularly relates to biomass-based hard carbon composite materials prepared based on the quantitative preparation of hard carbon pore volume, as well as the method thereof, negative electrode materials and batteries. Background Technology

[0002] Sodium is an extremely abundant element (ranked fourth in abundance among metallic elements in the Earth's crust) and is inexpensive. As a member of the same group as lithium, sodium shares similar chemical properties with lithium, making sodium-ion batteries a potential alternative to lithium-ion batteries in large-scale energy storage applications. However, graphite cannot form thermodynamically stable compounds with sodium, thus it cannot be used as the anode material for sodium-ion batteries, making the anode material a major limiting factor in their development. After 2000, the application of hard carbon as an anode material for sodium-ion batteries rekindled hope for their commercialization, making it the preferred anode material.

[0003] Hard carbon is carbon that cannot be graphitized after high-temperature treatment above 2800℃, while soft carbon is carbon that can be graphitized after high-temperature treatment. Hard carbon has a disordered internal crystal arrangement, more pores, and sodium storage capacity (over 300 mAh / g) due to its ability to store sodium in the interlayers of graphite sheets, closed micropores, surfaces, and defect sites, but its initial coulombic efficiency is lower. Soft carbon can be produced using petroleum coke, anthracite, and pitch, offering a significant cost advantage, but its sodium storage capacity is lower (approximately 250 mAh / g), making it less economically viable than hard carbon. Currently, hard carbon anode materials are mostly derived from biomass. While biomass sources are widespread, the variety of biomass and its seasonality make consistency difficult to guarantee. Furthermore, different biomass types require different production processes, increasing the complexity of process and equipment selection. The current industry requirements for hard carbon are a reversible capacity greater than 300 mAh / g and an initial charge-discharge efficiency greater than 90% [Chemical Engineering Journal, 2025, 511, 161953], which places high demands on the preparation process and raw material selection for hard carbon. Summary of the Invention

[0004] This invention addresses the problems of low initial coulombic efficiency, insufficient plateau capacity, and inconsistent product quality due to variations in raw material sources associated with traditional hard carbon materials. The aim of this invention is to provide a biomass-based hard carbon composite material, its method, anode material, and battery prepared by quantitatively analyzing the pore volume of hard carbon. This invention can significantly improve the consistency of biomass-based hard carbon materials and enhance their reversible capacity and initial coulombic efficiency. The product can be used in sodium-ion and lithium-ion batteries.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first objective of this invention is to provide a method for quantitatively preparing biomass-based hard carbon composite materials based on the pore volume of hard carbon, comprising the following steps: Before use, the biomass powder is washed with a dilute acid solution to uniformly disperse the pore-forming agent in the biomass powder, thus obtaining a precursor. Specifically, the pore-forming agent is dissolved in water to obtain a pore-forming agent solution; the biomass powder is then immersed in the solution and dried to remove moisture, yielding the precursor. Preferably, the biomass powder is a novel green energy source, processed from various plant biomass materials, specifically cellulose powder, bamboo powder, peanut shell powder, wood powder, wheat straw, corn stalks, etc.; the pore-forming agent is at least one of H3PO4, ZnCl2, KOH, and K2CO3.

[0006] The precursor was pre-carbonized under a protective gas, and after washing, a porous carbon matrix was obtained. The total pore volume of the porous carbon matrix was measured. Preferably, the pre-carbonization temperature was 500~900 °C, and the time was 1~2 h. The total pore volume of the porous carbon matrix was 0.20~0.65 cm³. 3 / g, a larger pore volume corresponds to a larger specific surface area. When soft carbon precursors (such as asphalt dissolved in a solvent) are mixed with a porous carbon matrix, a porous carbon with a high specific surface area means it has more developed internal channels and a larger internal surface. This allows the liquid asphalt precursor to penetrate deeper and spread more evenly on the inner and outer surfaces of the carbon matrix through capillary action. Furthermore, a high specific surface area directly corresponds to more surface defects and edge carbon atoms. These sites are chemically active and more prone to cross-linking reactions with asphalt; however, when the pore volume is too large, it means more asphalt is needed to "fill the gaps." This directly leads to an increase in raw material costs. An extremely high specific surface area means that the carbon matrix has a very strong adsorption effect on the asphalt solution, which may lead to local agglomeration, making it difficult for the asphalt to disperse evenly and penetrate deep into all pores, easily causing uneven filling and forming independent soft carbon regions. The interfacial bonding force between this soft carbon and the hard carbon matrix may be weak, failing to form an effective synergistic effect, resulting in a decrease in total capacity. The protective gas is one or a mixture of N2, Ar, and CO2.

[0007] A soft carbon precursor and a porous carbon matrix are dispersed in a solvent with a volume ratio of the soft carbon precursor to the total pore volume of the porous carbon matrix of (1.2-1.5):1, resulting in a mixture. When the volume ratio of the asphalt to the total pore volume of the porous carbon matrix is ​​too low, the specific surface area and pore volume of the carbonized material are large, which increases the irreversible decomposition of the electrolyte in the first cycle and the formation of a thicker SEI film, leading to a decrease in the first coulombic efficiency. When the volume ratio of the asphalt to the total pore volume of the porous carbon matrix is ​​too high, if the amount of asphalt added exceeds the amount required for the complete reaction of its -OH with the -COOH of the carbon matrix, the excess asphalt will not be able to bind to the carbon matrix through strong chemical bonds because all the active reaction sites (-COOH) on the surface of the carbon matrix have been occupied. The defects caused by excessive asphalt will irreversibly consume the electrolyte and lithium / sodium ions, leading to a decrease in the first coulombic efficiency. These soft carbon layers may block the pores that are originally conducive to ion transport, increasing the resistance to ion migration and resulting in a deterioration in rate performance. Preferably, the solvent is a liquid that has good solubility for the soft carbon precursor.

[0008] The solvent in the mixture is removed to obtain a dried material; the dried material is then carbonized to obtain a biomass-based hard carbon composite material.

[0009] As a preferred technical solution, the soft carbon precursor is asphalt and its derivatives; the asphalt is high softening point asphalt with a temperature of 150-280℃. This type of asphalt has a high residual carbon content, and at high temperatures, it is conducive to the formation of a larger microcrystalline structure.

[0010] As a preferred technical solution, the carbonization temperature is 1100~1500 ℃ and the time is 1~3 h.

[0011] A second objective of the present invention is to provide a biomass-based hard carbon composite material prepared by the method described in the first objective above; the biomass-based hard carbon composite material includes a porous carbon matrix and a soft carbon material filling the pores of the porous carbon matrix and coating the outer layer of the porous carbon matrix; the soft carbon precursor coating and / or filling the biomass porous hard carbon matrix transforms the open pores on the biomass porous hard carbon matrix into closed pores of 0.35~1.25 nm.

[0012] A third objective of the present invention is to provide a negative electrode material comprising the biomass-based hard carbon composite material as described in the second objective above.

[0013] A fourth object of the present invention is to provide a battery comprising the negative electrode material as described in the second object above.

[0014] The beneficial effects of this invention are as follows: The method provided by this invention first uniformly disperses a pore-forming agent in biomass powder, and after pre-carbonization and washing, obtains a porous carbon matrix. This step completes pore formation simultaneously with pre-carbonization, preparing a porous carbon matrix with a certain total pore volume. Subsequent steps, based on the total pore volume, design the amount of soft carbon precursor, enabling quantitative and rational use of soft carbon, resulting in consistent product performance and facilitating industrial production. Furthermore, it avoids the problem of inconsistent soft carbon raw material ratios due to the diversity of biomass sources.

[0015] This invention mixes a soft carbon precursor and a porous carbon matrix in a solvent, enabling the soft carbon precursor to effectively enter the pores inside the porous carbon matrix, thus laying the foundation for the soft carbon precursor to effectively fill the macropores in the porous carbon matrix during the subsequent carbonization step.

[0016] In the carbonization process, the soft carbon precursor and the porous carbon matrix undergo a certain chemical cross-linking reaction, which not only improves the residual carbon rate, but also constructs a unique structure rich in closed pores and ultra-micropores, effectively solving the problems of low initial coulombic efficiency and insufficient platform capacity of traditional hard carbon.

[0017] The biomass-based hard carbon composite material prepared by this invention is used as a negative electrode material in batteries, giving the batteries high reversible capacity and first coulombic efficiency, and has a promising market application prospect. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the formation of the soft and hard carbon composite material in the preparation example; Figure 2 Here is a CP-SEM image of the composite hard carbon material in Example 3; Figure 3 The infrared spectrum of Example 3; Figure 4 Thermogravimetric curve of the sample in Example 3; Figure 5 XPS images of samples from Examples 1-3 and Comparative Example 1; Figure 6 Thermogravimetric curves of the samples in Examples 1-3 and Comparative Example 1 are shown. Figure 7 The GCD curve of the negative electrode material in Comparative Example 1 is shown. Figure 8 This is the GCD curve of the negative electrode material in Example 1; Figure 9 This is the GCD curve of the negative electrode material in Example 2; Figure 10 This is the GCD curve of the negative electrode material in Example 3; Figure 11The GCD curve of the negative electrode material in Comparative Example 2 is shown. Figure 12 This is the GCD curve of the negative electrode material in Example 4; Figure 13 This is the GCD curve of the negative electrode material in Example 5; Figure 14 This is the GCD curve of the negative electrode material in Example 6; Figure 15 The electronic conductivity curves are for the samples in Examples 1-3 and Comparative Example 1. Detailed Implementation

[0019] In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments. However, those skilled in the art will understand that the invention can be practiced without these details. In other instances, well-known structures have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments. Unless the context otherwise requires, throughout the specification and appended claims, the word "comprising" should be interpreted in an open-ended, inclusive sense, i.e., as "including but not limited to".

[0020] This application provides a biomass-based hard carbon composite material. By activating pores with pore-forming agents such as ZnCl2, the pore volume of the biomass carbon is effectively increased. Then, a synergistic strategy is employed: filling the macropores of the biomass carbon with pitch and subsequently coating the pitch-filled biomass carbon. This process prepares a soft carbon-hard carbon composite anode material. The formation process can be found in [reference needed]. Figure 1 Indication.

[0021] Cellulose was purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Anhydrous ZnCl2 was purchased from Shanghai Maclean Biochemical Technology Co., Ltd. N-methylpyrrolidone (NMP) was purchased from Shenzhen Kejing Zhida Technology Co., Ltd. The asphalt (SAXD-250X) was purchased from Shenzhen Kejing Zhida Technology Co., Ltd.

[0022] Comparative Example 1 A method for preparing a biomass-based hard carbon composite material includes the following steps: Step 1. After drying 10g of cellulose, pre-carbonize it by calcining it in a tube furnace under a nitrogen atmosphere at a rate of 5℃ / min to 800℃ for 2 hours. Step 2. After removing the pre-carbonized product, place it in a beaker, add an appropriate amount of 1 M hydrochloric acid, and ultrasonically clean for 20 min. Then soak for 2 h and wash with water to remove impurities from the product, obtaining the pre-carbonized sample Cel. 0.103 The measured pore volume was 0.192 cm³. 3 / g,; Step 3. The pre-carbonized sample obtained after acid washing in Step 2 was heated to 1300℃ at a rate of 5℃ / min under an argon atmosphere and carbonized for 2 hours. After washing and drying with deionized water, the pore volume was measured to be 0.103 cm³. 3 / g, this sample is named Cel 0.103 -1300; Step 4. Select a density of 1.0 g / cm³ 3 The pre-carbonized Cel obtained after acid washing in step 2 is made from asphalt (PC). 0.103 The samples and asphalt were dissolved in NMP at mass ratios of 1:0.1, 1:0.2, and 1:0.3, respectively, with the NMP to asphalt mass ratio being 3:1. Step 5. Dry all samples from Step 4 in an 80 °C forced-air drying oven for 12 h until NMP is completely evaporated, to obtain Cel. 0.103 Mixtures with asphalt, such as mixtures (ACel) 0.103 / asphalt=1:0.3,w / w); Step 6. The sample from Step 5 is heated to 1300 °C at a rate of 5 °C / min and carbonized for 2 h under an argon atmosphere to obtain the hard carbon material Cel. 0.103 -PC(1:0.1), Cel 0.103 -PC(1:0.2), Cel 0.103 -PC(1:0.3).

[0023] Comparative Example 2 A method for preparing pitch-based carbon materials includes the following steps: Step 1. Heat 10g of dried asphalt to 1300℃ at 5℃ / min under an argon atmosphere and keep it at that temperature for 2 hours to obtain a sample named PC-1300.

[0024] Comparative Example 3 A method for preparing a biomass-based hard carbon material includes the following steps: Step 1. 10g of dried cellulose was heated to 1300℃ at 5℃ / min under an argon atmosphere and carbonized for 2 h to obtain a sample named Cel-1300.

[0025] Example 1 A method for preparing a biomass-based hard carbon composite material includes the following steps: Step 1. Soak 10g of dried cellulose and 5g of zinc chloride in 60g of deionized water, and heat and stir at 110℃ for 2 hours to ensure thorough mixing; Step 2. Dry the cellulose powder thoroughly impregnated with zinc chloride to remove moisture, and obtain the precursor; Step 3. The precursor from Step 2 is heated from 25°C to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere and held for 2 hours. After natural cooling in the furnace, the sample is taken out to obtain the pre-carbonized sample. Step 4. Place the pre-carbonized sample from Step 3 in a beaker, add an appropriate amount of 1 M hydrochloric acid, and ultrasonically clean for 20 min. Then soak for 2 h, followed by water washing to remove impurities from the product, yielding a pore volume of 0.279 cm³. 3 / g porous carbon matrix ACel 0.21 Further, the pre-carbonized sample ACl 0.21 Sample ACl was obtained by carbonization at 1300℃ for 2 hours under an argon atmosphere with a heating rate of 5°C / min. 0.21 -1300, its pore volume is 0.21 cm. 3 / g; Step 5. Select a density of 1.0 g / cm³. 3 The asphalt, the porous carbon matrix ACl from step 4 0.21 The asphalt was dispersed in NMP at mass ratios of 1:0.21, 1:0.31 and 1:0.41, respectively, where the mass ratio of NMP to asphalt was 3:1. Step 6. Dry all samples from Step 5 in an 80 °C forced-air drying oven for 12 h until NMP is completely evaporated to obtain ACl. 0.21 With asphalt mixtures, such as mixtures (ACel) 0.21 / asphalt=1:0.41,w / w); Step 7. The sample from Step 6 is heated to 1300 °C at a rate of 5 °C / min and carbonized for 2 h under an argon atmosphere to obtain the composite hard carbon material ACel. 0.21 -PC(1:0.21),ACel 0.21 -PC(1:0.31),ACel 0.21 -PC(1:0.41).

[0026] Example 2 A method for preparing a biomass-based hard carbon composite material includes the following steps: Step 1. Soak 10g of dried cellulose and 10g of zinc chloride in 60g of deionized water, and heat and stir at 110℃ for 2 hours to ensure thorough mixing; Step 2. Dry the cellulose powder thoroughly impregnated with zinc chloride to remove moisture, and obtain the precursor; Step 3. The precursor from Step 2 is heated from 25°C to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere and held for 2 hours. After natural cooling in the furnace, the sample is taken out to obtain the pre-carbonized sample. Step 4. Place the pre-carbonized sample from Step 3 in a beaker, add an appropriate amount of 1 M hydrochloric acid, and ultrasonically clean for 20 min. Then soak for 2 h, followed by water washing to remove impurities from the product, yielding a pore volume of 0.454 cm³. 3 / g porous carbon matrix ACel 0.43 Further, ACl 0.43 Sample ACl was obtained by carbonization at 1300℃ for 2 hours under an argon atmosphere with a heating rate of 5℃ / min. 0.43 -1300, the pore volume was measured to be 0.43 cm³. 3 / g; Step 5. Select a density of 1.0 g / cm³. 3 The asphalt, the porous carbon matrix ACl from step 4 0.43 The asphalt was dispersed in NMP at mass ratios of 1:0.43, 1:0.53 and 1:0.63, respectively, where the mass ratio of NMP to asphalt was 3:1. Step 6. Dry all samples from Step 5 in an 80 °C forced-air drying oven for 12 h until NMP is completely evaporated to obtain ACl. 0.43 Mixtures with asphalt, such as mixtures (ACel) 0.43 / asphalt=1:0.63,w / w); Step 7. The sample from Step 6 is heated to 1300 °C at a rate of 5 °C / min and carbonized for 2 h under an argon atmosphere to obtain the composite hard carbon material ACel. 0.43 -PC(1:0.43), ACl 0.43 -PC(1:0.53), ACl 0.43 -PC(1:0.63).

[0027] Example 3 A method for preparing a biomass-based hard carbon composite material includes the following steps: Step 1. Soak 10g of dried cellulose and 15g of zinc chloride in 60g of deionized water, and heat and stir at 110℃ for 2 hours to ensure thorough mixing; Step 2. Dry the cellulose powder thoroughly impregnated with zinc chloride to remove moisture, and obtain the precursor; Step 3. The precursor from Step 2 is heated from 25°C to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere and held for 2 hours. After natural cooling in the furnace, the sample is taken out to obtain the pre-carbonized sample. Step 4. Place the pre-carbonized sample from Step 3 in a beaker, add an appropriate amount of 1 M hydrochloric acid, and ultrasonically clean for 20 min. Then soak for 2 h, followed by water washing to remove impurities from the product, yielding a pore volume of 0.658 cm⁻¹. 3 / g porous carbon matrix ACel0.6 Further, ACl 0.6 The sample was carbonized at 1300℃ for 2 hours under an argon atmosphere by heating at a rate of 5℃ / min to obtain sample ACl. 0.6 At -1300°C, its pore volume was measured to be 0.6 cm³. 3 / g; Step 5. Select a density of 1.0 g / cm³. 3 The asphalt, the porous carbon matrix ACl from step 4 0.6 The NMP was dispersed in NMP with asphalt at mass ratios of 1:0.2, 1:0.6, 1:0.7, 1:0.8 and 1:1, respectively, with the mass ratio of NMP to asphalt being 3:1. Step 6. Dry all samples from Step 5 in an 80 °C forced-air drying oven for 12 h until NMP is completely evaporated to obtain ACl. 0.6 Mixtures with asphalt, such as mixtures (ACel) 0.6 / asphalt=1:0.6, w / w), mixture (ACel) 0.6 / asphalt=1:0.8, w / w), mixture (ACel) 0.6 / asphalt=1:1,w / w); Step 7. The sample from Step 6 is heated to 1300℃ at a rate of 5℃ / min and carbonized for 2 h under an argon atmosphere to obtain the hard carbon material ACel. 0.6 -PC(1:0.2), ACl 0.6 -PC(1:0.6), ACl 0.6 -PC(1:0.7), ACl 0.6 -PC(1:0.8), ACl 0.6 -PC(1:1).

[0028] Example 4 A method for preparing a biomass-based hard carbon composite material includes the following steps: Step 1. Soak 15g of dried cellulose and 20g of zinc chloride in 60g of deionized water, and heat and stir at 110℃ for 2 hours to mix them thoroughly; Step 2. Dry the cellulose powder thoroughly impregnated with zinc chloride to remove moisture, and obtain the precursor; Step 3. The precursor from Step 2 is heated from 25°C to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere and held for 2 hours. After natural cooling in the furnace, the sample is taken out to obtain the pre-carbonized sample. Step 4. Place the pre-carbonized sample from Step 3 in a beaker, add an appropriate amount of 1 M hydrochloric acid, and ultrasonically clean for 20 min. Then soak for 2 h and wash with water to remove impurities from the product, obtaining porous carbon matrix ACel. 0.66The sample was further carbonized at 1300℃ for 2 hours under an argon atmosphere by heating at 5℃ / min to obtain sample ACl. 0.66 -1300 (pore volume 0.66 cm) 3 / g); Step 5. Select a density of 1.0 g / cm³. 3 The asphalt, the porous carbon matrix ACl from step 4 0.66 The NMP was dispersed in NMP at mass ratios of 1:0.66, 1:0.86 and 1:1.06, respectively, where the mass ratio of NMP to NMP was 3:1. Step 6. Dry all samples from Step 5 in an 80°C forced-air drying oven for 12 h until NMP is completely evaporated; Step 7. The sample from Step 6 is heated to 1300 °C at a rate of 5 °C / min and carbonized for 2 h under an argon atmosphere to obtain the composite hard carbon material ACel. 0.66 -PC(1:0.66), ACl 0.66 -PC(1:0.86), ACl 0.66 -PC(1:1.06).

[0029] Example 5 A method for preparing a biomass-based hard carbon composite material includes the following steps: Step 1. Soak 10g of dried peanut shells and 15g of zinc chloride in 60g of deionized water, and heat and stir at 110℃ for 2 hours to ensure thorough mixing; Step 2. Dry the cellulose powder thoroughly impregnated with zinc chloride to remove moisture, and obtain the precursor; Step 3. The precursor from Step 2 is heated from 25°C to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere and held for 2 hours. After natural cooling in the furnace, the sample is taken out to obtain the pre-carbonized sample. Step 4. Place the pre-carbonized sample from Step 3 in a beaker, add an appropriate amount of 1 M hydrochloric acid, and ultrasonically clean for 20 min. Then soak for 2 h and wash with water to remove impurities from the product, obtaining porous carbon-based APS. 0.46 ; Step 5. The APS obtained after acid washing in Step 4 0.46 The sample was carbonized at 1300℃ for 2 hours under an argon atmosphere at a heating rate of 5°C / min, and the pore volume was measured to be 0.46 cm³. 3 / g, this sample is named APS 0.46 -1300; Step 6. Select a density of 1.0 g / cm³. 3 The asphalt, the porous carbon matrix APS of step 4 0.46The NMP was dispersed in NMP with asphalt at mass ratios of 1:0.26, 1:0.46, 1:0.66, 1:0.86 and 1:1.06, respectively, wherein the mass ratio of NMP to asphalt was 3:1. Step 7. Dry all samples from Step 6 in an 80°C forced-air drying oven for 12 h until NMP is completely evaporated; Step 8. The sample from Step 7 is heated to 1300 °C at a rate of 5 °C / min and carbonized for 2 h under an argon atmosphere to obtain the hard carbon material APS. 0.46 -PC(1:0.26), APS 0.46 -PC(1:0.46), APS 0.46 -PC(1:0.66), APS 0.46 -PC(1:0.86), APS 0.46 -PC(1:1.06).

[0030] Example 6 A method for preparing a biomass-based hard carbon composite material includes the following steps: Step 1. Soak 10g of dried bamboo shavings and 15g of zinc chloride in 60g of deionized water, and heat and stir at 110℃ for 2 hours to ensure thorough mixing; Step 2. Dry the bamboo shavings powder thoroughly impregnated with zinc chloride to remove moisture, and obtain the precursor; Step 3. The precursor from Step 2 is heated from 25 °C to 800 °C at a heating rate of 5 °C / min under a nitrogen atmosphere and held at that temperature for 2 hours. After natural cooling in the furnace, the sample is taken out to obtain the pre-carbonized sample. Step 4. Place the pre-carbonized sample from Step 3 in a beaker, add an appropriate amount of 1 M hydrochloric acid, and ultrasonically clean for 20 min. Then soak for 2 h and wash with water to remove impurities from the product, obtaining porous carbon matrix ABS. 0.603 ; Step 5. The pre-carbonized sample obtained after acid washing in Step 4 was carbonized at 1300℃ for 2 hours under an argon atmosphere at a heating rate of 5℃ / min. The pore volume was measured to be 0.603 cm³. 3 / g, this sample is named ABS 0.60.3 -1300; Step 6. Select a density of 1.0 g / cm³. 3 The asphalt, the porous carbon matrix ABB from step 4 0.603 The NMP and asphalt were dispersed in NMP at mass ratios of 1:0.2, 1:0.4, 1:0.6, 1:0.8 and 1:1, respectively, with the mass ratio of NMP to asphalt being 3:1. Step 7. Dry all samples from Step 6 in an 80 °C forced-air drying oven for 12 h until NMP is completely evaporated; Step 8. The sample from Step 7 is heated to 1300 °C at a rate of 5 °C / min and carbonized for 2 h under an argon atmosphere to obtain hard carbon material ABS. 0.603 -PC(1:0.2), ABS 0.603 -PC(1:0.4), ABS 0.603 -PC(1:0.6), ABS 0.603 -PC(1:0.8).

[0031] Characterization and analysis: (1) Figure 1 This is a schematic diagram of the soft and hard carbon composite material structure in the preparation example.

[0032] (2) The microstructure of the hard carbon material cross-section in the electrode was studied using a cross-sectional polished scanning electron microscope (CPSEM, Gatan Ilion II 697, USA). The microstructure of the negative electrode material in Example 3 was observed. See details. Figure 2 The characteristics of the negative electrode material cross-section can be observed, ACl 0.6 Numerous through-holes exist within -1300, and during the high-temperature carbonization process, ACl... 0.6 The PC(x) samples reveal soft carbon from bitumen filling / permeating the internal channels of porous carbon, ultimately forming a three-dimensional interconnected hard-soft carbon network structure. Simultaneously, the strong cross-linking between bitumen and porous carbon effectively promotes the formation of closed pores.

[0033] (3) In order to study the reaction mechanism between porous carbon matrix and pitch, we used Fourier transform infrared spectroscopy (FTIR, Nicolet iS50, Thermo Fisher Scientific, USA) to detect the reaction between cellulose and ACl. 0.6 And the existing forms of functional groups on the asphalt surface. For example... Figure 3 As shown, cellulose and ACl 0.6 At 3347 cm -1 A characteristic peak corresponding to the stretching vibration of the hydroxyl group appeared at 1620 cm⁻¹. -1 and 1450 cm -1 A stretching vibration peak representing the aromatic skeleton appeared at 1059 cm⁻¹. -1 and 1170 cm -1 A stretching vibration peak of the -C─O─C- bond was detected at 2901 cm⁻¹. However, after activation, the intensity of the -C=C- and -C─O─C- vibrational bonds in cellulose decreased, corresponding to the -CH2- and -CH3- bonds at 2901 cm⁻¹. -1and 1641 cm -1 The vibrational peak disappeared. This indicates that the presence of ZnCl2 promoted the dehydration and aromatization reactions, leading to the removal of hydroxyl groups and other aliphatic structures. Furthermore, a 1720 cm⁻¹ peak appeared in ACl. -1 The -C=O vibrational peak indicates that cellulose undergoes aliphatic cleavage and oxidation to form carboxyl groups. In the FTIR spectrum of bitumen, the hydroxyl group is at 3461 cm⁻¹. -1 A significant vibrational peak is observed at this location, indicating the presence of abundant aromatic phenolic structures in the asphalt. 0.6 The -COOH groups in the asphalt undergo a chemical cross-linking reaction with the -OH groups in the asphalt, forming abundant ester groups (-C(O)O-), which tightly bind the asphalt and cellulose. This chemical cross-linking reaction increases the disorder of HC and produces abundant closed-cell structures, thereby increasing the Na+ content in the low-pressure plateau region. + Storage capacity.

[0034] (4) In order to further investigate the interaction between the porous carbon matrix and pitch during the pyrolysis process, we tested the ACl in Example 3 under a N2 atmosphere. 0.6 Asphalt and its mixtures (ACel) 0.6 Thermogravimetric analysis (TGA, TG-DTA8122, Rigaku, Japan) was performed on a mixture of bitumen and asphalt at a ratio of 1:0.8 (w / w). The results are as follows: Figure 4 As shown, ACel 0.6 The residual carbon contents of asphalt and asphalt in a nitrogen atmosphere at 900℃ were 73.80% and 47.68%, respectively. The weight loss of asphalt between 400℃ and 500℃ was mainly due to the loss of volatile matter. (ACel) 0.6 The residual carbon content of the asphalt mixture (1:0.8, w / w) reached as high as 87.94%, exceeding that of ACl. 0.6 The residual carbon content of asphalt alone was also observed. The mixture did not exhibit the significant weight loss decrease trend observed when asphalt was pyrolyzed alone in the 400-500°C range, indicating that ACl and asphalt interacted during pyrolysis, altering their respective thermal behaviors. This once again provides direct evidence of the cross-linking reaction that occurred between the two.

[0035] (5) To gain a deeper understanding of the surface chemical properties, X-ray photoelectron spectroscopy (XPS, Thermo Fisher Scientific, USA) analysis was performed to distinguish the configuration of the O atoms. The O 1s spectrum was fitted to the OI peak (533.4 eV), O-II peak (532.1 eV), and O-III peak (531.7 eV). The OI peak corresponds to carboxyl and ester groups (-COOH, -COOR), the O-II peak corresponds to phenol, hydroxyl, and ether groups (C─OH, -C─O─C-), and the OIII peak corresponds to hydrocarbons related to carbonyl groups (C=O). Fourier transform infrared spectroscopy and thermogravimetric analysis have confirmed a successful chemical cross-linking reaction between the carbon matrix and the pitch. XPS analysis revealed the formation of ester groups after cross-linking during the carbonization process. Figure 5 The O 1s spectrum in the image shows that it is similar to Cel. 0.103 -PC(1:0.3)(34.06%), ACl 0.21 -PC(1:0.41) (35.49%) and ACl 0.43 Compared to -PC(1:0.63) (41.43%), ACel 0.6 -PC (1:0.8) has the highest OI peak percentage (53.29%), indicating that a larger specific surface area will form a stronger and more extensive chemical crosslink with asphalt, thereby forming more ester groups and exhibiting superior microstructure (closed-cell / ultra-microporous) and macroscopic properties (specific capacity, first coulombic efficiency, conductivity).

[0036] (6) To further investigate the interaction between porous carbon matrices with different specific surface areas and pitch during pyrolysis, we performed thermogravimetric analysis (TGA, TG-DTA8122, Rigaku, Japan) on samples from Examples 1-3 and Comparative Example 1 under a N2 atmosphere. The results are as follows: Figure 6 As shown, the mixture (ACel) 0.103 The mixture (asphalt / asphalt = 1:0.3, w / w) has a residual carbon content of 65.87% under nitrogen atmosphere at 900℃. 0.21 The mixture (asphalt / asphalt = 1:0.41, w / w) has a residual carbon content of 81.08% under nitrogen atmosphere at 900℃. 0.43 The mixture (asphalt / asphalt ratio 1:0.63, w / w) has a residual carbon content of 85.76% under nitrogen atmosphere at 900℃. 0.6 The residual carbon content of the composite material (asphalt = 1:0.8, w / w) was 87.94% under nitrogen atmosphere at 900℃. This further verifies that the cross-linking reaction between the porous carbon matrix with high specific area and the asphalt was more complete, resulting in a more stable composite material structure.

[0037] Mixture (ACel) 0.6The mixture (asphalt / asphalt ratio 1:0.6, w / w) has a residual carbon content of 84.64% under nitrogen atmosphere at 900℃. 0.6 The residual carbon content of the mixture (asphalt = 1:0.8, w / w) at 900℃ under a nitrogen atmosphere is 87.94%. 0.6 The residual carbon content of asphalt (w / w) at 900℃ under nitrogen atmosphere was 77.23%, indicating that adding an appropriate amount of asphalt containing -OH groups is sufficient to consume the -COOH groups in the carbon matrix to form ester groups during the chemical crosslinking reaction. However, adding too much asphalt may result in excess asphalt existing independently, leading to a decrease in the overall carbonization rate.

[0038] Half-cells were made using the negative electrode materials from Examples 1-3 and Comparative Examples 1-3: Anode slurry was prepared by mixing 94.5 wt% of anode material, 1.5 wt% of carbon black (CB), 1.5 wt% of sodium carboxymethyl cellulose (CMC), and 2.5 wt% of styrene-butadiene rubber (SBR) in an aqueous solution.

[0039] The negative electrode slurry was then uniformly cast onto the copper foil, with the mass loading of the active material maintained at 1 and 4.5 mg / cm³, respectively. 2 Then, the electrode was dried in a vacuum oven at 90 °C for 12 hours to obtain the negative electrode sheet. Sodium metal foil was used as the counter electrode, 1M NaFP6 dissolved in diethylene glycol dimethyl ether (DEGDME) was used as the electrolyte, and glass fiber (GF / D) purchased from Whatman was used as the separator. The assembly process was carried out in a glove box (H2O, O2 < 0.1 ppm).

[0040] (7) Electrochemical testing GCD values ​​were measured by the BTS3000 battery testing system at 0.001–2.5 V.

[0041] Based on pore volume, the effect of adding different masses of asphalt on its performance was studied. Half-point cell assembly was performed on all materials, and the initial constant current charge-discharge curves of each electrode at 20 mA / g were obtained, as shown below. Figure 7 As shown, Cel 0.103 -1300, Cel 0.103 -PC(1:0.1), Cel 0.103 -PC(1:0.2), Cel 0.103 The initial charge capacities of the -PC(1:0.3) negative electrode were 124.22, 293.63, 272.29, and 285.67 mAh / g, respectively. Among them, Cel... 0.103 The -PC(1:0.3) anode exhibits the highest initial coulombic efficiency (89.57%), significantly outperforming Cel. 0.103-1300 (78.55%). In Figure 8 Chinese ACI 0.21 -1300, ACl 0.21 -PC(1:0.21),ACel 0.21 -PC(1:0.31),ACel 0.21 The initial charge capacities of the -PC(1:0.41) negative electrode were 90.17, 336.92, 335.91, and 318.03 mAh / g, respectively. Among them, ACl... 0.21 -PC(1:0.31),ACel 0.21 The -PC(1:0.41) anode exhibits excellent initial coulombic efficiency of 90.12% and 90.85%, significantly outperforming ACel. 0.21 -1300 (64.78%).

[0042] Compared with Comparative Example 1, the hard carbon material prepared in Example 1 showed significantly improved performance, indicating that the use of a pore-forming agent for pre-carbonization in this invention enriched the pore structure of the pre-carbonized material and significantly increased the specific surface area of ​​the pre-carbonized material (porous carbon matrix). Subsequent asphalt filling and coating carbonization treatment can further improve the pore structure of the material, resulting in a high-performance composite hard carbon material. The pore volume data of the pre-carbonized material tested in this process can serve as a quantitative basis for the amount of asphalt added.

[0043] Based on the previous examples, we further optimized the effect of asphalt content on the properties of composite hard carbon made from porous carbon matrices with different pore volumes. This was done based on the initial constant current charge-discharge curves of each electrode at 20 mA / g, as follows: Figure 9 The ACl shown 0.43 -1300, ACl 0.43 -PC(1:0.43), ACl 0.43 -PC(1:0.53), ACl 0.43 The initial charge capacities of the -PC(1:0.63) negative electrode were 92.01, 317.82, 322.75, and 358.77 mAh / g, respectively. Among them, ACl... 0.43 The -PC(1:0.63) anode exhibits the highest initial coulombic efficiency (90.32%), significantly outperforming ACel. 0.43 -1300 (65.20%). In Figure 10 and Figure 11 Chinese ACI 0.6 -1300, PC-1300, ACl 0.6 -PC(1:0.2), ACl 0.6 -PC(1:0.6), ACl 0.6 -PC(1:0.7), ACl 0.6-PC(1:0.8), ACl 0.6 The initial charge capacities of the -PC (1:1) negative electrode were 116.38, 152.95, 144.47, 339.82, 332.32, 361.04, and 321.96 mAh / g, respectively. Among them, ACl... 0.6 The -PC(1:0.8) anode exhibits a very high initial coulombic efficiency (92.04%), significantly better than ACel. 0.6 -1300 (72.23%) and PC-1300 (47.07%). ACel 0.6 The -PC(1:0.2) sample, due to insufficient asphalt, could not effectively convert open pores with poor sodium storage into closed pores with high sodium storage efficiency, resulting in insufficient plateau capacity from closed-pore filling. Further increasing the asphalt content may lead to excess asphalt existing independently, increasing material defects, such as those found in ACl. 0.6 The PC(1:1) sample showed a decrease in both specific capacity and initial coulombic efficiency. This was observed in samples with a pore volume of 0.66 cm³. 3 The same trend was also observed in the / g sample, such as Figure 12 As shown, ACel 0.66 -PC(1:0.66), ACl 0.66 -PC(1:0.86), ACl 0.66 The initial charge capacities of the -PC(1:1.06) anode were 322.53, 314.41 and 268.3 mAh / g, respectively, and the initial coulombic efficiencies were 88.79, 91.27 and 90.14%, respectively.

[0044] The feasibility of the experimental method will continue to be verified using other biomass materials, such as... Figure 13 As shown, different proportions of asphalt were used to composite the electrodes. Based on the initial constant current charge-discharge curves of each electrode at 20 mA / g, the APS... 0.46 -1300, APS 0.46 -PC(1:0.26), APS 0.46 -PC(1:0.46), APS 0.46 -PC(1:0.66), APS 0.46 -PC(1:0.86), APS 0.46 The initial charge capacities of the -PC(1:1.06) anode were 255.71, 249.31, 259.58, 328.76, 290.89, and 265.95 mAh / g, respectively, with initial coulombic efficiencies of 83.67, 85.86, 89.11, 90.49, 85.19, and 83.6%, respectively. Porous carbon matrices were prepared from bamboo chips and then composited with different proportions of pitch. Figure 14The first constant current charge-discharge curves of each electrode at 20 mA / g are shown in the ABS diagram. 0.603 -1300, ABS 0.603 -PC(1:0.2), ABS 0.603 -PC(1:0.4), ABS 0.603 -PC(1:0.6), ABS 0.603 The initial charge capacities of the -PC (1:0.8) were 247.36, 274.38, 275.2, 310.55 and 351.21 mAh / g, respectively, and the initial coulombic efficiencies were 80.05, 86.8, 86.66, 90.362 and 92.18%, respectively.

[0045] Table 1 shows the initial coulombic efficiency and charging capacity test results of representative hard carbon materials in Examples 1-4 and Comparative Example 1. From the data trend in Table 1, it can be seen that as the total pore volume of the porous carbon matrix increases, the optimal ratio of bitumen volume fraction to the total pore volume of the porous carbon matrix decreases. Combined with the pore volume data of the porous carbon matrix pre-carbonized at 800℃ and after further carbonization at 1300℃ for 2 hours (see Table 2), the presence of the pore-forming agent zinc chloride enhances the degree of condensation reaction during biomass carbonization, reduces the number of functional groups reacting with bitumen in the porous carbon matrix, thereby reducing the amount of bitumen used for the crosslinking reaction; simultaneously, ACel... 0.6 -PC(1:0.8) material has optimal capacity and coulombic efficiency; further increasing the pore volume results in the composite material ACl. 0.66 -PC (1:0.86) exhibited a decrease in both capacity and coulombic efficiency, indicating that a larger pore volume in the porous carbon matrix is ​​not necessarily better. Furthermore, preparing a high-pore-volume matrix requires an increased amount of pore-forming agent, leading to higher costs for both the agent and environmental impact, as well as an increase in the total amount of bitumen used. Therefore, considering both cost and performance, controlling the pore volume of the porous carbon matrix within the range of 0.20-0.65 cm⁻¹ is preferable. 3 The ratio of the asphalt volume fraction to the total pore volume of the porous carbon matrix should ideally be controlled within the range of 1.2-1.5. Peanut shell composite carbon APS 0.46 -PC (1:0.66) and bamboo composite carbon ABS 0.603 The experimental results of -PC(1:0.8) also conform to this trend.

[0046] Table 1. Initial coulombic efficiency and charge capacity of representative hard carbon materials in Examples 1-4 and Comparative Example 1

[0047] Table 2. Pore volume data of carbon materials after pre-carbonization at 800℃ and further carbonization at 1300℃ of biomass

[0048] (8) Electronic conductivity test Further electronic conductivity testing was performed using an electrode resistance meter (BER1300, Xiamen Yuaneng), such as... Figure 15 As shown, Cel 0.103 At 60 MPa, the electronic conductivity of Cel is only 0.35 S / cm. 0.103 -PC(1:0.1), Cel 0.103 -PC(1:0.2), Cel 0.103 -PC(1:0.3) exhibits electronic conductivity of 10.51, 11.95, and 12.78 S / cm under the same pressure. ACel 0.21 At -1300 MPa, the electronic conductivity is 5.54 S / cm, ACel 0.21 -PC(1:0.21),ACel 0.21 -PC(1:0.31),ACel 0.21 -PC(1:0.41) exhibits electronic conductivity of 13.94, 13.86, and 13.65 S / cm under the same pressure. ACel 0.43 At -1300 MPa, the electronic conductivity is 4.22 S / cm, ACel 0.43 -PC(1:0.43), ACl 0.43 -PC(1:0.53), ACl 0.43 -PC(1:0.63) exhibits electronic conductivity of 12.27, 13.97, and 15.97 S / cm under the same pressure. At 60 MPa, ACl... 0.6 The electronic conductivity of -1300 is 3.31 S / cm, while that of PC-1300 is 12.41 S / cm. (ACel) 0.6 -PC(1:0.6), ACl 0.6 -PC(1:0.8), ACl 0.6 The electronic conductivity of PC (1:1) under the same pressure is 16.80, 18.67, and 19.12 S / cm. The low conductivity of pure cellulose hard carbon stems from its inherently highly disordered and defective microstructure. However, by combining it with asphalt, the high conductivity and continuous network formed after asphalt carbonization compensates for the structural defects of biomass carbon, acting as a "bridge" for electron transport, resulting in a qualitative leap in the electronic conductivity of the composite material. The improvement in the electronic conductivity of the material also significantly helps to improve its rate performance.

[0049] Table 3. Specific surface area and pore volume parameters of samples from Examples 1-6 and Comparative Examples 1-3 calculated using the BET method based on N2 adsorption / desorption isotherms.

[0050] Table 3 shows the specific surface area and pore volume parameters of the samples in Examples 1-6 and Comparative Examples 1-3 calculated using the BET method based on N2 adsorption / desorption isotherms. Table 3 shows that the specific surface area of ​​Cel-1300 (without pore-forming agent) is 387.749 m². 2 / g, while after using a pore-forming agent, ACl 0.6 With a specific surface area of ​​-1300, it reaches as high as 1100.051 m². 2 / g, pore volume from 0.165 cm 3 / g increased to 0.601 cm 3 / g. This demonstrates that the pore-forming agent successfully created an extremely well-developed porous structure in biomass carbon. After asphalt coating, the specific surface area and pore volume of the material decreased by orders of magnitude. ACel 0.6 -1300 to ACl 0.6 -PC(1:0.8): Specific surface area drops sharply from 1100.051 to 7.126 m² 2 / g; pore volume decreased sharply from 0.601 to 0.0137 cm³. 3 / g. This directly proves that the asphalt almost completely fills most of the pores inside the porous carbon matrix and forms an effective coating layer on its outside. This process transforms a highly active porous framework with a huge specific surface area into a composite material with extremely low surface area and a dense structure. When the asphalt content is further increased, ACl 0.6 -PC(1:1) specific surface area (3.082 m²) 2 / g) and pore volume (0.0108 cm³) 3 The / g) dropped to a minimum. Combined with the electrochemical data (capacity and first-response decline), this indicates overfilling. Excessive bitumen may have formed an excessively thick, isolated soft carbon layer, which not only blocked beneficial ion channels but also introduced new side reaction sites due to its numerous defects.

[0051] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for quantitative preparation of biomass-based hard carbon composite based on hard carbon pore volume, characterized by, The method comprises the following steps: uniformly dispersing a pore-forming agent in biomass powder to obtain a precursor; pre-carbonizing the precursor in a protective gas, and obtaining a porous carbon matrix after washing and drying; measuring the total pore volume of the porous carbon matrix; dispersing the soft carbon precursor and the porous carbon matrix in a solvent, wherein the volume ratio of the soft carbon precursor to the total pore volume of the porous carbon matrix is (1.2-1.5):1, to obtain a mixture; removing the solvent in the mixture to obtain a dry material; and carbonizing the dry material to obtain a biomass-based hard carbon composite material.

2. The method for preparing a biomass-based hard carbon composite material based on hard carbon pore volume quantification according to claim 1, characterized by, The biomass powder is cleaned with a dilute acid solution before use; and the method for uniformly dispersing the pore-forming agent in the biomass powder comprises the following steps: dissolving the pore-forming agent in water to obtain a pore-forming agent solution, immersing the biomass powder in the pore-forming agent solution, and then drying to remove water to obtain the precursor.

3. The method for preparing a biomass-based hard carbon composite material based on hard carbon pore volume quantification according to claim 1, characterized in that, The pore-forming agent is at least one of H3PO4, ZnCl2, KOH, and K2CO3.

4. The method for preparing a biomass-based hard carbon composite material based on hard carbon pore volume quantification according to claim 1, characterized in that, The pre-carbonization is performed at a temperature of 500-900 ℃ for 1-2 h.

5. The method for preparing a biomass-based hard carbon composite material based on hard carbon pore volume quantification according to claim 1, characterized in that, The total pore volume of the porous carbon matrix is in the interval of 0.20 - 0.65 cm3 / g. 3 / g.

6. The method for preparing a biomass-based hard carbon composite material based on hard carbon pore volume quantification according to claim 1, characterized in that, The soft carbon precursor is pitch and its derivatives; and the softening point of the pitch is 150-280 ℃.

7. The method for preparing a biomass-based hard carbon composite material based on hard carbon pore volume quantification according to claim 1, characterized by, The carbonization is performed at a temperature of 1100-1500 ℃ for 1-3 h.

8. A biomass-based hard carbon composite material, characterized by, The biomass-based hard carbon composite material is prepared by the method according to any one of claims 1 to 7; and the biomass-based hard carbon composite material comprises a porous carbon matrix and a soft carbon material filled in the pores of the porous carbon matrix and coated on the outside of the porous carbon matrix.

9. A negative electrode material, characterized by, The negative electrode material comprises the biomass-based hard carbon composite material according to claim 8.

10. A battery, characterized by The battery comprises the negative electrode material according to claim 9.

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