Preparation method and application of composite hard carbon material based on crop straw and coal coking byproducts

Abstract

This paper discloses a method for preparing and applying composite hard carbon materials based on crop straw and coal coking by-products, relating to the field of new energy materials technology. The method uses crop straw and coal tar (a coal coking by-product) as raw materials. The crop straw is pre-carbonized in air to retain its natural three-dimensional tubular framework and form a porous network, then mixed and impregnated with liquid coal tar, and finally carbonized at high temperature in an inert atmosphere. The liquid coal tar deeply penetrates the pores of the straw and transforms into dense amorphous graphite domains at high temperature, physically filling and stitching the open macropores of the straw, transforming the loose open pores into sodium-storing closed pores, and reshaping it into a dense, robust 3D interconnected bulk structure. This invention abandons the traditional and cumbersome acid-base impurity removal and pore-forming process. It utilizes the dense coating and in-situ reinforcement of liquid coal tar to reduce the specific surface area of ​​the material and improve the first coulombic efficiency and compaction density. It effectively solves the pain points of low first efficiency and poor energy density of traditional biomass hard carbon. The preparation process is simple, environmentally friendly, and low in cost, and it is easy to realize the large-scale industrialization of sodium-ion battery anode materials.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, and in particular to a method for preparing and applying a composite hard carbon material based on crop straw and coal coking by-products. Background Technology

[0002] Currently, billions of tons of crop straw are generated globally each year, with my country alone having a theoretical annual resource volume exceeding 800 million tons. However, the current utilization of this type of biomass resource is relatively extensive, mainly relying on direct burning, inefficient fuel production, or natural return to the fields. This not only causes serious resource waste but also exacerbates greenhouse gas and particulate matter emissions, leading to environmental problems. Under the "dual carbon" strategic goal, exploring high-value-added utilization and efficient carbon sequestration pathways for agricultural waste is of great significance. Converting the carbon elements in biomass into structurally stable advanced carbon materials can not only effectively prevent carbon oxidation and escape but also provide a low-cost carbon source for the new energy industry, achieving a win-win situation for both environmental benefits and economic value.

[0003] Meanwhile, in the field of large-scale energy storage, sodium-ion batteries are becoming the next-generation electrochemical energy storage technology with the greatest potential for large-scale application due to their low resource costs and excellent low-temperature / rate performance. However, the industrialization process of sodium-ion batteries is constrained by the lack of anode materials that combine low cost and high performance. Hard carbon, due to its structural diversity and high sodium storage capacity, is widely recognized as the most ideal commercial anode material.

[0004] Crop straw, as an abundant and renewable biomass precursor, is rich in carbohydrates and lignin and possesses a natural three-dimensional porous structure. Furthermore, the trace metal elements it contains (such as K, Ca, and Mg) have a certain activating effect on the carbon skeleton during pyrolysis, making it an ideal carbon source for preparing hard carbon materials. Converting straw into hard carbon anodes for sodium-ion batteries not only meets the demand for low-cost precursors in the energy storage field but also provides an effective way to achieve high-value carbon sequestration from agricultural waste. However, the intense gas production during the pyrolysis of single straw results in a thin hard carbon skeleton with excessive open pores, leading to bottlenecks in practical applications such as low initial coulombic efficiency, insufficient compaction density, and poor batch-to-batch consistency. Therefore, it is urgent to introduce composite modification and structural reshaping strategies to effectively overcome the intrinsic structural defects of crop straw-based hard carbon while achieving biomass resource utilization.

[0005] To address the aforementioned structural defects, this invention introduces low-cost liquid coal tar (rich in polycyclic aromatic hydrocarbons and phenols) as a structure modifier. Leveraging its excellent wettability, the coal tar undergoes dehydration condensation and electrophilic substitution reactions with oxygen-containing functional groups on the pretreated straw matrix, constructing a stable COC and CC covalent crosslinked network in situ. Simultaneously, the coal tar component chelates in situ with trace metals within the crop straw, effectively supporting the carbon skeleton and widening the carbon interlayer spacing, providing a low-resistance transport channel for sodium ions. Through the synergistic effect of crosslinking and chelation, the coal tar deeply fills and seals the open macropores of the straw, transforming the originally loose matrix into a smooth, dense three-dimensional interconnected network. This molecular-level structural reshaping promotes the transformation from disordered open pores to nanopores, effectively avoiding the disadvantage of a single straw skeleton being prone to collapse, achieving simultaneous improvements in material efficiency, capacity, and compaction density, and providing a practical solution for the large-scale preparation of low-cost, high-performance sodium electrode anodes. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the primary objective of this invention is to provide a composite hard carbon anode material based on crop straw and coal coking byproducts. The most significant scientific feature of this material is its use of crop straw and liquid coal tar as raw materials to construct a synergistic mechanism of impregnation-filling, molecular cross-linking, and in-situ chelation. Electron-rich polycyclic aromatic hydrocarbons in the coal tar undergo dehydration and condensation with oxygen-containing functional groups on the surface of the pretreated straw, forming a robust COC and CC cross-linked network. Simultaneously, the carbon chains of the coal tar form metal-organic chelates with the trace metals (K, Ca, Mg, etc.) native to the straw. This dual action deeply stitches together the originally disordered open macropores of the crop straw, precisely reshaping them into a smooth, dense 3D closed-pore structure. This structure aligns with the sodium ion storage mechanism, inhibiting the formation of irreversible solid-state electrolyte interfaces, thereby improving the battery's initial coulombic efficiency and sodium storage capacity.

[0007] This invention provides a method for preparing and applying a composite hard carbon material based on crop straw and coal coking by-products. The core steps are as follows: First, the crop straw is pre-carbonized in air to retain its natural 3D channels and graft abundant oxygen-containing functional groups onto the pore surface. Then, it is mixed with low-cost coal tar in a certain mass ratio. Utilizing capillary effect, the liquid coal tar deeply impregnates and fills the pores of the straw, transforming the material from a loose powder into a moist, dense mixture. Finally, it is carbonized at high temperature under an inert atmosphere. The coal tar within the pores undergoes in-situ pyrolysis at high temperature and deeply cross-links with the straw matrix, generating dense amorphous graphite domains that seal the open channels. This process eliminates the cumbersome acid-base purification steps, achieving efficient carbon fixation of agricultural straw waste while significantly reducing preparation costs. Its concise process provides a practical solution for the large-scale production of high-performance sodium-ion battery hard carbon anodes.

[0008] Firstly, the preparation method of the hard carbon anode material is as follows:

[0009] Step 1): Pre-carbonize the crop straw to obtain pre-carbonized material.

[0010] Step 2): The crop straw in Step 1) is one or more of corn cobs, wheat straw, corn straw and rice straw and their derivatives.

[0011] Step 3): The pre-carbonization temperature in Step 1) is 150-600 ℃, the pre-sintering time is 1-24 h, and the heating rate is 1-10 ℃ / min.

[0012] Step 4): Mix the pre-carbonized material obtained in Step 3) with coal tar, a by-product of coal coking, to obtain a mixture material. The mixing mass ratio of pre-carbonized crop straw biomass to coal tar is 9:1-1:9.

[0013] Step 5): Combine the mixture from step 4) using one or more of the following methods: mechanical stirring, mortar and pestle grinding, planetary ball milling, or mechanical kneading.

[0014] Step 6): The mixture powder obtained in step 4) is heated to 800-1600 ℃ under an inert atmosphere, the carbonization time is 1-10 h, and the heating rate is 1-100 ℃ / min to obtain the hard carbon material. The inert atmosphere is at least one of nitrogen or argon.

[0015] Secondly, a composite hard carbon anode material made from crop straw and coal coking by-products is prepared using the method and application described in the first aspect.

[0016] Thirdly, a sodium-ion battery negative electrode sheet.

[0017] This includes the composite hard carbon anode material made from crop straw and coal coking byproducts as described in the second aspect.

[0018] Fourthly, a sodium-ion secondary battery.

[0019] This includes the negative electrode sheet described in the third aspect.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) This invention provides a composite hard carbon anode material based on crop straw and coal coking by-products. Coal tar is rich in polycyclic aromatic hydrocarbons (PAHs). When mixed with pre-carbonized crop straw and pyrolyzed at high temperature, the two undergo molecular-level cross-linking reinforcement. Simultaneously, the carbon chains of coal tar form in-situ metal-organic chelates with the trace metals (K, Ca, Mg, etc.) native to the straw. Liquid coal tar deeply penetrates and physically fills the disordered open pores of the straw, reshaping them into dense closed pores for sodium storage and effectively expanding the interlayer spacing of carbon microcrystals. By controlling the precursor ratio and process, the pore structure and surface chemical properties can be optimized, significantly improving the sodium storage activity of the material from a microscopic mechanism.

[0022] (2) This invention provides a method for preparing and applying a composite hard carbon material based on crop straw and coal coking by-products. This composite material, as the negative electrode of a sodium-ion battery, exhibits high initial efficiency, high capacity, and excellent cycle stability. Its dense closed-cell structure significantly reduces the specific surface area, inhibiting the formation of an irreversible solid electrolyte interface. The robust carbon skeleton constructed through in-situ reinforcement with coal tar effectively overcomes the defects of traditional straw hard carbon structures, such as loose structure and excessive absorption of electrolyte, thereby improving the energy density of the electrode. At the same time, the widened carbon interlayer spacing constructs a low-resistance sodium ion transport channel, further releasing the sodium storage capacity of the material in the low potential plateau region.

[0023] (3) This invention uses agricultural straw and coal coking by-products as raw materials to achieve high-value carbon sequestration and conversion of waste, which is in line with the "dual carbon" strategic orientation. In terms of process design, this method eliminates the cumbersome and costly acid-base purification steps. At the same time, relying on the high residual carbon rate of coal tar, it effectively makes up for the disadvantage of low yield of single straw, and significantly reduces the overall manufacturing cost. In addition, the deep wetting of liquid coal tar effectively homogenizes the physical differences of straw precursors, ensuring batch consistency of products. This preparation process is simple and environmentally friendly, and highly compatible with existing industrial heat treatment equipment, providing a practical and feasible technical solution for the large-scale production of low-cost sodium-ion battery anodes. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope (SEM) image of the hard carbon material prepared in Example 1.

[0025] Figure 2 This is the charge-discharge curve for the first week of Example 1.

[0026] Figure 3 This is a graph showing the 0.2 C cycle performance of Example 1 in a sodium-ion battery.

[0027] Figure 4 This is a scanning electron microscope (SEM) image of the hard carbon material prepared in Example 2.

[0028] Figure 5 This is the charge-discharge curve for the first week of Example 2.

[0029] Figure 6 This is a graph showing the 0.2 C cycle performance of Example 2 in a sodium-ion battery.

[0030] Figure 7 This is a scanning electron microscope (SEM) image of the hard carbon material prepared in Example 3.

[0031] Figure 8 This is the charge-discharge curve for the first week of Example 3.

[0032] Figure 9 This is a graph showing the 0.2 C cycle performance of Example 3 in a sodium-ion battery.

[0033] Figure 10 This is a scanning electron microscope (SEM) image of the hard carbon material prepared in Example 4.

[0034] Figure 11 This is the charge-discharge curve for the first week of Example 4.

[0035] Figure 12 This is a graph showing the 0.2 C cycle performance of Example 4 in a sodium-ion battery.

[0036] Figure 13 This is a scanning electron microscope (SEM) image of the hard carbon material prepared in Example 5.

[0037] Figure 14 Charge-discharge curves for the first week of Example 5.

[0038] Figure 15 This is a graph showing the 0.2 C cycle performance of Example 5 in a sodium-ion battery.

[0039] Figure 16 This is a scanning electron microscope (SEM) image of the hard carbon material prepared in Example 6.

[0040] Figure 17 This is the charge-discharge curve for the first week of Example 6.

[0041] Figure 18 This is a graph showing the 0.2 C cycle performance of Example 6 in a sodium-ion battery.

[0042] Figure 19 This is a scanning electron microscope (SEM) image of the hard carbon material prepared in Example 7.

[0043] Figure 20 This is the charge-discharge curve for the first week of Example 7.

[0044] Figure 21 This is a graph showing the 0.2 C cycle performance of Example 7 in a sodium-ion battery.

[0045] Figure 22This is a scanning electron microscope (SEM) image of the hard carbon material prepared in Example 8.

[0046] Figure 23 This is the charge-discharge curve for the first week of Example 8.

[0047] Figure 24 This is a graph showing the 0.2 C cycle performance of Example 8 in a sodium-ion battery.

[0048] Figure 25 This is a scanning electron microscope (SEM) image of the hard carbon material prepared in Comparative Example 1.

[0049] Figure 26 This is the charge-discharge curve for the first week of comparison example 1.

[0050] Figure 27 This is a graph showing the 0.2 C cycle performance of Comparative Example 1 in a sodium-ion battery. Detailed Implementation

[0051] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0052] Example 1

[0053] This embodiment provides a method for preparing and applying composite hard carbon materials based on crop straw and coal coking by-products.

[0054] The preparation steps are as follows: First, the crushed corn cobs are placed in an air atmosphere and heated to 250 ℃ at a heating rate of 5 ℃ / min and held for 12 h. This pre-carbonization process retains the natural porous network of the straw and grafts oxygen-containing functional groups onto its surface. After cooling, a dry and loose pre-carbonized powder is obtained. The pre-carbonized corn cobs and liquid coal tar at room temperature are accurately weighed and added to a mechanical stirring device at a mass ratio of 7:3 and mixed thoroughly. Under the action of mechanical shearing and capillary action, the liquid coal tar deeply coats and infiltrates the pores of the pre-carbonized corn cobs, and the macroscopic morphology of the material changes from a dry powder that is easily blown away to a dark brown moist agglomerate with a certain degree of adhesion. The mixed material with the above-described morphological transformation is transferred to a tube furnace and heated to 1300 ℃ at a heating rate of 3 ℃ / min under an argon atmosphere and held for 3 h. During the high-temperature sintering stage, the coal tar that has penetrated into the pores undergoes in-situ pyrolysis, deeply cross-links with the matrix, and fills the open channels. After natural cooling, crushing, and sieving, a composite hard carbon material of crop straw and coal coking by-products with a dense surface, robust skeleton, and rich closed-pore structure is obtained.

[0055] Figure 1 The image is a scanning electron microscope (SEM) image of the composite hard carbon material made from crop straw and coal coking by-products described in Example 1. It can be clearly seen that it is composed of objects of irregular shapes and different sizes.

[0056] Assembly and electrochemical performance testing of button batteries:

[0057] The prepared composite hard carbon anode material of crop straw and coal coking by-products was mixed with conductive carbon black and carboxymethyl cellulose at a mass ratio of 90:5:5. A suitable amount of deionized water was added dropwise to the mixture, and after stirring, a uniform slurry was formed. The slurry was coated onto copper foil and vacuum dried at 80 °C for 12 hours. Anode sheets with a diameter of 11 mm were then cut. Using sodium metal as the counter electrode, a glass fiber filter membrane (Whatman GF / C) as the separator, a 1 mol / L NaPF6 solution in dimethyl ethylene glycol (DME) as the electrolyte, and a stainless steel shell as the outer casing, a 2025 button cell was assembled. Charge-discharge tests were conducted using the Xinwei battery system, with a test voltage range of 0.01-2.0 V and a test temperature of room temperature. The test current density for the first three cycles was 0.1 C (1 C = 300 mA / g), followed by charge-discharge tests at a current density of 0.2 C.

[0058] Experimental results: The reversible specific capacity in the first cycle was 258.72 mAh / g ( Figure 2 The initial coulombic efficiency was 83.91%, the median voltage was 0.078 V, and the specific capacity after 130 cycles was 230.59 mAh / g. Figure 3 ).

[0059] Example 2

[0060] This embodiment provides a method for preparing and applying composite hard carbon materials based on crop straw and coal coking by-products.

[0061] The preparation steps are as follows: First, the crushed corn cobs are placed in an air atmosphere and heated to 250 ℃ at a heating rate of 5 ℃ / min and held for 12 h. This pre-carbonization process retains the natural porous network of the straw and grafts oxygen-containing functional groups onto its surface. After cooling, a dry and loose pre-carbonized powder is obtained. The pre-carbonized corn cobs and liquid coal tar at room temperature are accurately weighed and added to a mechanical stirring device at a mass ratio of 3:7 and mixed thoroughly. Under the action of mechanical shearing and capillary action, the liquid coal tar deeply coats and infiltrates the pores of the pre-carbonized corn cobs, and the macroscopic morphology of the material changes from a dry powder that is easily blown away to a dark brown moist agglomerate with a certain degree of adhesion. The mixed material with the above-mentioned morphological transformation is transferred to a tube furnace and heated to 1300 ℃ at a heating rate of 3 ℃ / min under an argon atmosphere and held for 3 h. During the high-temperature sintering stage, the coal tar that has penetrated into the pores undergoes in-situ pyrolysis, deeply cross-links with the matrix, and fills the open channels. After natural cooling, crushing, and sieving, a composite hard carbon material of crop straw and coal coking by-products with a dense surface, robust skeleton, and rich closed-pore structure is obtained.

[0062] Figure 4 The image is a scanning electron microscope (SEM) image of the composite hard carbon material made from crop straw and coal coking by-products described in Example 2. It can be clearly seen that it is composed of irregularly shaped objects of varying sizes, with fine broken particles interspersed among them.

[0063] As in Example 1, electrodes were prepared, batteries were assembled, and electrochemical tests were performed.

[0064] Experimental results: The reversible specific capacity in the first cycle was 245.98 mAh / g ( Figure 5 The initial coulombic efficiency was 82.12%, the median voltage was 0.0803 V, and the specific capacity after 130 cycles was 230.59 mAh / g. Figure 6 ).

[0065] Example 3

[0066] This embodiment provides a method for preparing and applying composite hard carbon materials based on crop straw and coal coking by-products.

[0067] The preparation steps are as follows: First, the pulverized wheat straw is placed in an air atmosphere and heated to 250 °C at a heating rate of 5 °C / min and held for 12 h. This pre-carbonization process retains the natural porous network of the straw and grafts oxygen-containing functional groups onto its surface. After cooling, a dry and loose pre-carbonized powder is obtained. The pre-carbonized wheat straw and liquid coal tar at room temperature are accurately weighed and added to a mechanical stirring device at a mass ratio of 7:3 and mixed thoroughly. Under the action of mechanical shearing and capillary action, the liquid coal tar deeply encapsulates and infiltrates the pores of the pre-carbonized wheat straw, and the macroscopic morphology of the material changes from a dry powder that is easily blown away to a dark brown moist agglomerate with a certain degree of adhesion. The mixed material with the above-mentioned morphological transformation is transferred to a tube furnace and heated to 1300 °C at a heating rate of 3 °C / min under an argon atmosphere and held for 3 h. During the high-temperature sintering stage, the coal tar that has penetrated into the pores undergoes in-situ pyrolysis, deeply cross-links with the matrix, and fills the open channels. After natural cooling, crushing, and sieving, a composite hard carbon material of crop straw and coal coking by-products with a dense surface, robust skeleton, and rich closed-pore structure is obtained.

[0068] Figure 7 The image is a scanning electron microscope (SEM) image of the composite hard carbon material made from crop straw and coal coking by-products described in Example 3. The material exhibits a distinctly irregular blocky and fragmented morphology. At the same time, a large number of fine debris with a size of several micrometers or even submicrometers are scattered and aggregated around and in the gaps between these large particles.

[0069] As in Example 1, electrodes were prepared, batteries were assembled, and electrochemical tests were performed.

[0070] Experimental results: The reversible specific capacity in the first cycle was 241.89 mAh / g ( Figure 8 The initial coulombic efficiency was 82.20%, the median voltage was 0.0817 V, and the specific capacity after 170 cycles was 182.28 mAh / g. Figure 9 ).

[0071] Example 4

[0072] This embodiment provides a method for preparing and applying composite hard carbon materials based on crop straw and coal coking by-products.

[0073] The preparation steps are as follows: First, the pulverized wheat straw is placed in an air atmosphere and heated to 250 °C at a heating rate of 5 °C / min and held for 12 h. This pre-carbonization process retains the natural porous network of the straw and grafts oxygen-containing functional groups onto its surface. After cooling, a dry and loose pre-carbonized powder is obtained. The pre-carbonized wheat straw and liquid coal tar at room temperature are accurately weighed and added to a mechanical stirring device at a mass ratio of 3:7 and mixed thoroughly. Under the action of mechanical shearing and capillary action, the liquid coal tar deeply encapsulates and impregnates the pores of the pre-carbonized wheat straw, and the macroscopic morphology of the material changes from a dry powder that is easily blown away to a dark brown moist agglomerate with a certain degree of adhesion. The mixed material with the above-mentioned morphological transformation is transferred to a tube furnace and heated to 1300 °C at a heating rate of 3 °C / min under an argon atmosphere and held for 3 h. During the high-temperature sintering stage, the coal tar that has penetrated into the pores undergoes in-situ pyrolysis, deeply cross-links with the matrix, and fills the open channels. After natural cooling, crushing, and sieving, a composite hard carbon material of crop straw and coal coking by-products with a dense surface, robust skeleton, and rich closed-pore structure is obtained.

[0074] Figure 10 The image is a scanning electron microscope (SEM) image of the composite hard carbon material made from crop straw and coal coking by-products described in Example 4. The material shows a large number of particles of varying sizes and irregular shapes, along with spherical particles.

[0075] As in Example 1, electrodes were prepared, batteries were assembled, and electrochemical tests were performed.

[0076] Experimental results: The reversible specific capacity in the first cycle was 244.84 mAh / g ( Figure 11 The initial coulombic efficiency was 82.27%, the median voltage was 0.0786 V, and the specific capacity after 160 cycles was 207.42 mAh / g. Figure 12 ).

[0077] Example 5

[0078] This embodiment provides a method for preparing and applying composite hard carbon materials based on crop straw and coal coking by-products.

[0079] The preparation steps are as follows: First, the crushed corn stalks are placed in an air atmosphere and heated to 250 °C at a heating rate of 5 °C / min and held for 12 h. This pre-carbonization process retains the natural porous network of the stalks and grafts oxygen-containing functional groups onto their surface. After cooling, a dry and loose pre-carbonized powder is obtained. The pre-carbonized corn stalks and liquid coal tar at room temperature are accurately weighed and added to a mechanical stirring device at a mass ratio of 7:3 and mixed thoroughly. Under the action of mechanical shearing and capillary action, the liquid coal tar deeply coats and impregnates the pores of the pre-carbonized corn stalks, and the macroscopic morphology of the material changes from a dry powder that is easily blown away to a dark brown moist agglomerate with a certain degree of adhesion. The mixed material with the above-mentioned morphological transformation is transferred to a tube furnace and heated to 1300 °C at a heating rate of 3 °C / min under an argon atmosphere and held for 3 h. During the high-temperature sintering stage, the coal tar that has penetrated into the pores undergoes in-situ pyrolysis, deeply cross-links with the matrix, and fills the open channels. After natural cooling, crushing, and sieving, a composite hard carbon material of crop straw and coal coking by-products with a dense surface, robust skeleton, and rich closed-pore structure is obtained.

[0080] Figure 13 The image is a scanning electron microscope (SEM) image of the composite hard carbon material of crop straw and coal coking by-products described in Example 5. The material exhibits particles with regular pores, honeycomb-like or plant tissue cross-section structures, as well as irregular blocky and thick sheet-like particles.

[0081] As in Example 1, electrodes were prepared, batteries were assembled, and electrochemical tests were performed.

[0082] Experimental results: The reversible specific capacity in the first cycle was 233.84 mAh / g ( Figure 14 The initial coulombic efficiency was 78.15%, the median voltage was 0.097 V, and the specific capacity after 170 cycles was 190.42 mAh / g. Figure 15 ).

[0083] Example 6

[0084] This embodiment provides a method for preparing and applying composite hard carbon materials based on crop straw and coal coking by-products.

[0085] The preparation steps are as follows: First, the crushed corn stalks are placed in an air atmosphere and heated to 250 °C at a heating rate of 5 °C / min and held for 12 h. This pre-carbonization process retains the natural porous network of the stalks and grafts oxygen-containing functional groups onto their surface. After cooling, a dry and loose pre-carbonized powder is obtained. The pre-carbonized corn stalks and liquid coal tar at room temperature are accurately weighed and added to a mechanical stirring device at a mass ratio of 3:7 and mixed thoroughly. Under the action of mechanical shearing and capillary action, the liquid coal tar deeply encapsulates and infiltrates the pores of the pre-carbonized corn stalk powder, and the macroscopic morphology of the material changes from a dry powder that is easily blown away to a dark brown moist agglomerate with a certain degree of adhesion. The mixed material with the above-described morphological transformation is transferred to a tube furnace and heated to 1300 °C at a heating rate of 3 °C / min under an argon atmosphere and held for 3 h. During the high-temperature sintering stage, the coal tar that has penetrated into the pores undergoes in-situ pyrolysis, deeply cross-links with the matrix, and fills the open channels. After natural cooling, crushing, and sieving, a composite hard carbon material of crop straw and coal coking by-products with a dense surface, robust skeleton, and rich closed-pore structure is obtained.

[0086] Figure 16 The image is a scanning electron microscope (SEM) image of the composite hard carbon material of crop straw and coal coking by-products described in Example 6. The material exhibits aggregates with sponge-like or porous characteristics, while fine particles of a few micrometers are embedded in large particles of tens of micrometers and the gaps at their junctions.

[0087] As in Example 1, electrodes were prepared, batteries were assembled, and electrochemical tests were performed.

[0088] Experimental results: The reversible specific capacity in the first cycle was 225.89 mAh / g ( Figure 17 The initial coulombic efficiency was 81.88%, the median voltage was 0.0889 V, and the specific capacity after 150 cycles was 184.093 mAh / g. Figure 18 ).

[0089] Example 7

[0090] This embodiment provides a method for preparing and applying composite hard carbon materials based on crop straw and coal coking by-products.

[0091] The preparation steps are as follows: First, the crushed rice straw is placed in an air atmosphere and heated to 250 ℃ at a heating rate of 5 ℃ / min and held for 12 h. This pre-carbonization process retains the natural porous network of the straw and grafts oxygen-containing functional groups onto its surface. After cooling, a dry and loose pre-carbonized powder is obtained. The pre-carbonized rice straw and liquid coal tar at room temperature are accurately weighed and added to a mechanical stirring device at a mass ratio of 7:3 and mixed thoroughly. Under the action of mechanical shearing and capillary action, the liquid coal tar deeply encapsulates and infiltrates the pores of the pre-carbonized rice straw powder, and the macroscopic morphology of the material changes from a dry powder that is easily blown away to a dark brown moist agglomerate with a certain degree of adhesion. The mixed material with the above-mentioned morphological transformation is transferred to a tube furnace and heated to 1300 ℃ at a heating rate of 3 ℃ / min under an argon atmosphere and held for 3 h. During the high-temperature sintering stage, the coal tar that has penetrated into the pores undergoes in-situ pyrolysis, deeply cross-links with the matrix, and fills the open channels. After natural cooling, crushing, and sieving, a composite hard carbon material of crop straw and coal coking by-products with a dense surface, robust skeleton, and rich closed-pore structure is obtained.

[0092] Figure 19 The image is a scanning electron microscope (SEM) image of the composite hard carbon material made from crop straw and coal coking by-products described in Example 7. The material exhibits a large number of dense blocky shapes with fractures, and is interspersed with many rough-surfaced and irregularly shaped carbon fragments.

[0093] As in Example 1, electrodes were prepared, batteries were assembled, and electrochemical tests were performed.

[0094] Experimental results: The reversible specific capacity in the first cycle was 202.10 mAh / g ( Figure 20 The initial coulombic efficiency was 77.08%, the median voltage was 0.0958 V, and the specific capacity after 170 cycles was 164.17 mAh / g. Figure 21 ).

[0095] Example 8

[0096] This embodiment provides a method for preparing and applying composite hard carbon materials based on crop straw and coal coking by-products.

[0097] The preparation steps are as follows: First, the crushed rice straw is placed in an air atmosphere and heated to 250 ℃ at a heating rate of 5 ℃ / min and held for 12 h. This pre-carbonization process retains the natural porous network of the straw and grafts oxygen-containing functional groups onto its surface. After cooling, a dry and loose pre-carbonized powder is obtained. The pre-carbonized rice straw and liquid coal tar at room temperature are accurately weighed and added to a mechanical stirring device at a mass ratio of 3:7 and mixed thoroughly. Under the action of mechanical shearing and capillary action, the liquid coal tar deeply encapsulates and impregnates the pores of the pre-carbonized rice straw, and the macroscopic morphology of the material changes from a dry powder that is easily blown away to a dark brown moist agglomerate with a certain degree of adhesion. The mixed material with the above-mentioned morphological transformation is transferred to a tube furnace and heated to 1300 ℃ at a heating rate of 3 ℃ / min under an argon atmosphere and held for 3 h. During the high-temperature sintering stage, the coal tar that has penetrated into the pores undergoes in-situ pyrolysis, deeply cross-links with the matrix, and fills the open channels. After natural cooling, crushing, and sieving, a composite hard carbon material of crop straw and coal coking by-products with a dense surface, robust skeleton, and rich closed-pore structure is obtained.

[0098] Figure 22 The image is a scanning electron microscope (SEM) image of the composite hard carbon material made from crop straw and coal coking by-products described in Example 8. The material exhibits a structure with dense micropores in some areas, resembling a honeycomb or coarse tubes, and is accompanied by fine particles.

[0099] As in Example 1, electrodes were prepared, batteries were assembled, and electrochemical tests were performed.

[0100] Experimental results: The reversible specific capacity in the first cycle was 211.16 mAh / g ( Figure 23 The initial coulombic efficiency was 80.71%, the median voltage was 0.092 V, and the specific capacity after 170 cycles was 174.02 mAh / g. Figure 24 ).

[0101] Comparative Example 1

[0102] This comparative example provides coal tar-based hard carbon, its preparation method, and its applications.

[0103] The preparation steps are as follows: coal tar is directly heated to 1300 ℃ under an argon atmosphere at a heating rate of 3 ℃ / min and held for 3 h to obtain coal tar-based hard carbon.

[0104] Figure 25 This is a scanning electron microscope (SEM) image of the coal tar-based hard carbon material described in Comparative Example 1. The material is composed of a large number of fine particles.

[0105] As in Example 1, electrodes were prepared, batteries were assembled, and electrochemical tests were performed.

[0106] Experimental results: The specific capacity of the first discharge cycle was 193.30 mAh / g ( Figure 26 The initial coulombic efficiency was 52.28%, the median voltage was 0.1317 V, and the specific capacity after 150 cycles was 154.63 mAh / g. Figure 27 ).

Claims

1. A method for preparing and applying a composite hard carbon material based on crop straw and coal coking by-products, characterized in that, The crop straw is pre-carbonized in the air, and then the pre-carbonized crop straw is mixed with coal tar, a by-product of coal coking, in a certain mass ratio. After high-temperature carbonization in an inert atmosphere, a composite hard carbon anode material is obtained.

2. The preparation method according to claim 1, characterized in that, The pre-carbonization temperature of crop straw in air is 150-600 ℃, preferably 200-400 ℃; the time is 1-24 h, preferably 8-15 h; and the heating rate is 1-10 ℃ / min, preferably 4-8 ℃ / min.

3. The preparation method according to claim 1, characterized in that, Crop straw includes one or more of corn cobs, wheat straw, corn stalks, rice straw, and their derivatives.

4. The preparation method according to claim 1, characterized in that, The pre-carbonized crop straw is mixed with coal tar, a byproduct of coal coking, in a mass ratio of 9:1 to 1:9, preferably 9:1 to 3:7; the mixing is carried out by any one or more of the following methods: mechanical stirring, mortar grinding, planetary ball milling, or mechanical kneading.

5. The mixture of pre-carbonized crop straw and coal tar (a byproduct of coal coking) according to claim 4, characterized in that, After mixing, the coal tar, which is in a liquid state at room temperature, uniformly coats and impregnates the pores of the pre-carbonized biomass. The morphology of the mixture changes from a dry, loose powder to a dark brown, moist powder or an agglomerated substance with adhesive properties.

6. The preparation method according to claim 1, characterized in that, The high-temperature carbonization temperature is 800-1600 ℃, preferably 900-1400 ℃; the carbonization time is 1-10 h, preferably 2-4 h; the heating rate is 1-100 ℃ / min, preferably 2-5 ℃ / min; and the inert atmosphere is at least one of nitrogen or argon.

7. The application of the composite hard carbon material based on crop straw and coal coking by-products as described in claim 1, or the composite hard carbon material prepared by the method described in any one of claims 2-6, as a negative electrode material for sodium-ion batteries.

8. A negative electrode sheet for a sodium-ion battery, comprising: The sodium-ion battery composite hard carbon material made from crop straw and coal coking by-products as described in claim 1, a current collector, a binder coated on the current collector, a conductive agent, and the composite hard carbon material made from crop straw and coal coking by-products as described in any one of claims 2-6.

9. A sodium-ion secondary battery comprising the negative electrode of the sodium-ion battery according to claim 8.

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