A sodium-ion battery biomass-derived hard carbon negative electrode material and a preparation method and application thereof based on cross-linking pore-making

Abstract

The application discloses a kind of sodium ion battery biomass derived hard carbon negative electrode material and its preparation method and application based on crosslinking pore making, it is related to sodium ion battery technical field.Prepared by air oxidation and ammonium chloride catalytic dehydration crosslinking pore making process.The method is: first, air oxidation pretreatment is carried out to biomass, then mixed with ammonium chloride and dried, then low-temperature carbonization is carried out to make ammonium chloride decompose to form open nanopore, high-temperature carbonization is carried out to make open nanopore into closed pore structure, finally, after washing and drying, the final sodium ion battery biomass derived hard carbon negative electrode material is obtained.The method can improve the porosity of hard carbon material, optimize its pore structure, improve the efficiency of sodium ion transmission and storage, so that the material has the advantages of high specific capacity, high first coulomb efficiency, high rate performance and high energy density, and the process is simple, low in cost and environmentally friendly, solve the problems of low porosity of traditional hard carbon material in existing sodium ion battery negative electrode material, insufficient electrochemical performance and the like.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a sodium-ion battery biomass-derived hard carbon anode material and its preparation method and application based on cross-linking pore formation. Background Technology

[0002] With the increasing global demand for clean energy and sustainable energy storage, lithium-ion batteries face challenges in large-scale application due to the relative scarcity and uneven distribution of lithium resources, including cost and resource constraints. Sodium-ion batteries, as a novel energy storage system, demonstrate great potential in large-scale energy storage due to their abundant resources and low cost. The anode material is a key component of sodium-ion batteries, crucial to their performance. Hard carbon materials, with their disordered structure, large interlayer spacing, and abundant defect sites, are an ideal choice for sodium-ion battery anode materials. However, traditional hard carbon materials suffer from underdeveloped pore structures, leading to low sodium-ion transport and storage efficiency, low initial coulombic efficiency, and short plateau capacity, thus affecting the battery's rate performance and energy density, limiting its commercial application. Biomass carbon sources offer advantages such as wide availability, low cost, and controllable structure, making them ideal raw materials for preparing hard carbon anodes for sodium-ion batteries. However, direct carbonization can lead to morphological breakage and reduced compaction density, affecting electrochemical performance. How to prepare highly cross-linked, highly closed-cell, and high-specific-capacity hard carbon anodes through simple processing methods is a pressing problem to be solved.

[0003] Currently, numerous patents have explored the preparation of hard carbon anode materials, but all have limitations to varying degrees. For example, patent 201610414923.0 discloses a method for preparing soft carbon and hard carbon core-shell structure anode materials. It involves mixing ammonium chloride aqueous solution with starch, pre-carbonizing, carbonizing, and then using a specific coating agent to prepare a soft carbon / hard carbon composite core-shell structure hard carbon material. However, its limitations are mainly reflected in the following aspects: First, the core-shell interface compatibility is not ideal, failing to effectively suppress the formation of a large amount of SEI on the surface of the hard carbon core, resulting in low initial efficiency. Second, the spray drying process used to construct the shell layer makes the material porous, which, while beneficial for ion migration, sacrifices tap density, leading to insufficient volumetric energy density. Finally, the complex multilayer structure and high-temperature carbonization process amplify the preparation cost and voltage polarization problem. Therefore, the differences in structure and function between the core and shell fail to achieve efficient synergy, instead highlighting the contradiction between process and performance, limiting its commercial value. Furthermore, its application focuses on lithium-ion batteries, lacking in-depth research on compatibility with sodium-ion batteries. Patent 202110329645.X uses specific crosslinking agents and starch, emphasizing a segmented heating carbonization process to prepare hard carbon anode materials. It is also applied in the lithium-ion battery field, but does not specifically consider the special requirements of sodium-ion batteries. Patent 202211553612.4 uses soluble ammonium salts and carbon sources, and prepares hard carbon materials through spray granulation and sintering, carbonizing twice under a nitrogen atmosphere at 100-600℃ and 1000-1700℃. However, it does not precisely control the open / closed pore structure, resulting in a maximum initial reversible capacity of only 318.5 mAh / g when used as a sodium-ion battery anode material, which is insufficient to meet the requirements of high-performance sodium-ion batteries. Patent 202310892039.8 combines asphalt with starch, focusing on improving the poor performance caused by the uneven structure of asphalt-based hard carbon. However, it is insufficient in precisely controlling the closed-pore structure of hard carbon to improve the initial reversible specific capacity. The preparation process of patent 202411883263.1 is relatively complex, involving multiple steps such as organic acid esterification, oxidative crosslinking, and carbonization with phosphorus and nitrogen sources. Although it is dedicated to preparing starch-based hard carbon anodes for sodium-ion batteries, there is still room for improvement in the simplicity of the process and the precise control of the closed-pore structure.

[0004] In summary, existing technical solutions mainly focus on solving the technical problems related to lithium-ion battery anode materials. In this field, it is well known that although lithium-ion batteries and sodium-ion batteries operate on the same principle, there are fundamental differences in the compatibility of their anode materials. This means that the microstructure design principles of hard carbon materials suitable for lithium-ion batteries cannot usually be directly transferred to sodium-ion battery systems. For example, the most commonly used anode material for lithium-ion batteries is graphite (including natural and artificial graphite), but graphite anodes exhibit extremely low capacity in sodium-ion batteries and are essentially unusable (Chem. Rev. 2014, 114, 11636−11682: DOI: dx.doi.org / 10.1021 / cr500192f). Furthermore, when low-temperature treated carbon materials (hard and soft carbon) are used as anode materials for lithium-ion batteries, carbon anode materials carbonized at around 700 °C exhibit the highest lithium storage capacity, while sodium-ion battery hard carbon anodes generally show the best electrochemical performance when carbonized at around 1500 °C (Science 1995, 270 (5236)). 590-593; Adv. Energy Mater. 2020, 10(20) 2002704). This fully demonstrates that carbon materials that can be used as negative electrodes for lithium and sodium-ion batteries cannot be considered the same material. The two have essential and systematic differences in microstructure, surface properties, preparation process, energy storage mechanism, and required electrolyte environment, and cannot be used interchangeably. Therefore, this invention provides a biomass hard carbon material and its preparation method specifically designed for sodium-ion storage needs (such as the need for larger interlayer spacing and specific closed-pore structure). This is significantly different from existing technologies aimed at optimizing lithium-ion storage performance in terms of technical problems, solutions, and expected effects. In existing technologies for preparing hard carbon negative electrodes for sodium-ion batteries, although the material performance has been improved through esterification modification and activation pore formation, there are still problems such as complex processes, high costs, and insufficient electrochemical performance. Therefore, it is urgent to develop a simple, efficient, and cost-controllable bio-based hard carbon negative electrode material preparation method, which is of great significance for promoting the commercialization of sodium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a biomass-derived hard carbon anode material for sodium-ion batteries, its preparation method based on cross-linking pore formation, and its application. Through the synergistic effect of air oxidation pretreatment and ammonium chloride-catalyzed pore formation, the porosity of the hard carbon material is effectively increased, and the pore structure is optimized, thereby improving the transport and storage efficiency of sodium ions, enhancing the material's specific capacity, initial coulombic efficiency, and cycle stability. Simultaneously, the preparation process is simplified, and production costs are reduced. This invention addresses the problems of low porosity, small interlayer spacing, and insufficient electrochemical performance in existing hard carbon materials.

[0006] To achieve the above objectives, this invention discloses a method for preparing a biomass-derived hard carbon anode material for sodium-ion batteries based on cross-linking pore formation, comprising the following steps:

[0007] Step (1) Air oxidation oxidizes the hydroxyl groups on the biomass chain to carboxyl groups: Place the biomass material in an oxidation furnace and continuously introduce air at a flow rate of 100-5000 mL / min; raise the temperature to 150-350 ℃ and keep it at that temperature for 1-20 h;

[0008] Step (2) Ammonium chloride catalyzes the esterification and crosslinking of hydroxyl and carboxyl groups in biomass: The oxidized biomass material is mixed with ammonium chloride in deionized water and stirred evenly, and then dried at a temperature of 35-160 °C to obtain esterified biomass material;

[0009] Step (3) Low-temperature carbonization to create open pores: The esterified biomass material is placed in a carbonization furnace and heated to 500-900 ℃ under inert gas protection and kept at that temperature for 1-4 h. Ammonium chloride decomposes to produce NH3 and HCl gas, which escapes and forms an open nanoporous structure.

[0010] Step (4) High-temperature carbonization to create closed pores: The biomass material after low-temperature carbonization is placed in a carbonization furnace and heated to 1100-1600 ℃ under the protection of inert gas and kept at that temperature for 1-4 h to promote the transformation of some open nanopore structures into closed pore structures.

[0011] Step (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery biomass-derived hard carbon anode material.

[0012] The oxidation process involves oxidizing and cross-linking the precursor of biomass feedstock before carbonization to inhibit foaming and coalescence during carbonization, and is a key step in the preparation of hard char. During this process, microcrystalline chains in the precursor break down, and then slow dehydration and cross-linking occur between molecular chains through the escape of water. The oxygen functional groups in the biomass precursor can be altered by changing the oxidation temperature and time.

[0013] Preferably, in step (1), the biomass is selected from one or more of potato starch, corn starch, wheat starch, cassava starch, natural cellulose, microcrystalline cellulose, methyl cellulose, and fruit shells.

[0014] Preferably, in step (2), the mass ratio of biomass material to ammonium chloride is 1:(0.001-1).

[0015] The present invention also provides a sodium-ion battery biomass-derived hard carbon anode material prepared by the above preparation method, wherein the sodium-ion battery biomass-derived hard carbon anode material contains closed-pore nanopores and is used to prepare biomass-based sodium-ion battery hard carbon anode materials.

[0016] Therefore, the present invention employs the above-mentioned sodium-ion battery biomass-derived hard carbon anode material and its preparation method and application based on cross-linking pore formation, which has the following beneficial effects:

[0017] (1) This invention prepares a core-shell-free hard carbon material through a synergistic strategy of air oxidation pretreatment and ammonium chloride pore-forming, and achieves precise construction of pore structure and simultaneous control of surface chemistry in the hard carbon material. Air oxidation pre-activates the carbon skeleton, oxidizing some hydroxyl groups on the biomass chain to carboxyl groups, laying the foundation for subsequent crosslinking and pore-forming; ammonium chloride decomposes upon heating to produce ammonia (NH3) and hydrogen chloride (HCl) gases. HCl creates an acidic environment, catalyzing intramolecular and intermolecular dehydration of starch molecules, forming a stable three-dimensional crosslinked network structure, improving carbon yield and stabilizing the disordered skeleton of hard carbon. The decomposition gas acts as a pore-forming agent, generating abundant pore structures (open and closed pores) in the carbon matrix, providing space and channels for ion storage. At the same time, ammonium chloride, as a nitrogen-containing reagent, introduces nitrogen heteroatoms into the carbon matrix through its decomposition of nitrogen-containing species (such as NH3), effectively passivating surface defects and suppressing side reactions. This combined pore-forming process avoids structural collapse, eliminates the need for templates or strong etchants, and simultaneously optimizes the number of sodium-storing active sites and interface stability, providing a controllable synthesis route for high-performance hard carbon.

[0018] (2) The hard carbon anode prepared by the above preparation method has excellent performance: its hierarchical nanopores provide sodium storage active sites, which significantly improves the specific capacity of the material; the stable interface regulated by nitrogen doping significantly improves the initial coulombic efficiency of the prepared hard carbon material, which can reach more than 90% under preferred conditions (such as Examples 1, 16, and 18), greatly reducing active sodium loss; the well-developed microporous network accelerates ion diffusion, giving the material excellent rate performance; when matched with the positive electrode, it can improve the battery energy density and meet the requirements of long-term driving range. Moreover, the use of biomass as a precursor eliminates the need for complex equipment, making the material both low-cost and environmentally friendly, and possessing the potential for large-scale application.

[0019] (3) This invention combines air oxidation pretreatment with ammonium chloride catalytic crosslinking to create pores, and adopts a graded carbonization strategy of low-temperature open-pore and high-temperature closed-pore creation. This successfully achieves precise control over the pore structure of biomass hard carbon materials, realizing the transformation from open pores to closed pores, thereby improving the platform capacity and initial coulombic efficiency of sodium-ion battery anode materials. The optimized hard carbon material also exhibits high reversible capacity (up to 429.9 mAh / g), high initial coulombic efficiency (up to 90%), and excellent cycle stability (capacity retention rate of over 99.9% after 100 cycles) in specific embodiments (such as Example 6). The biomass-derived hard carbon anode material for sodium-ion batteries is suitable as an anode active material for sodium-ion batteries. When applied to sodium-ion battery half-cell testing, it exhibits excellent sodium storage performance. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of untreated raw corn starch used in Example 1 of the present invention.

[0021] Figure 2 A photograph of the corn starch-derived hard carbon anode material for sodium-ion batteries prepared in Example 1 of this invention.

[0022] Figure 3 This is a scanning electron microscope image of the corn starch-derived hard carbon anode material for sodium-ion batteries prepared in Example 1 of the present invention.

[0023] Figure 4 This is a high-resolution transmission electron microscope image of the corn starch-derived hard carbon anode material for sodium-ion batteries prepared in Example 1 of this invention.

[0024] Figure 5 The charge-discharge curve of the corn starch-derived hard carbon anode material for sodium-ion batteries prepared in Example 1 of this invention at a current density of 20 mAh / g is shown.

[0025] Figure 6 The cycling performance curves of the corn starch-derived hard carbon anode material prepared in Example 1 of this invention are shown at different current densities.

[0026] Figure 7 The rate performance curves of the corn starch-derived hard carbon anode material prepared in Example 1 of this invention are shown at different current densities.

[0027] Figure 8 This is a photograph of the carbonized starch-derived hard carbon anode material prepared in Comparative Example 1.

[0028] Figure 9 This is a scanning electron microscope image of the carbonized starch-derived hard carbon anode material prepared in Comparative Example 1.

[0029] Figure 10The image shows a scanning electron microscope image of the corn starch-derived hard carbon anode material for sodium-ion batteries, labeled a in Comparative Example 2.

[0030] Figure 11 The image shows a scanning electron microscope image of the corn starch-derived hard carbon anode material for sodium-ion batteries, numbered b in Comparative Example 2.

[0031] Figure 12 The image shows a scanning electron microscope image of the corn starch-derived hard carbon anode material for sodium-ion batteries, labeled c in Comparative Example 2.

[0032] Figure 13 This is a scanning electron microscope image of the sodium-ion battery pine nut shell-derived hard carbon anode material prepared in Example 8 of the present invention. Detailed Implementation

[0033] This invention provides a biomass-derived hard carbon anode material for sodium-ion batteries.

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0036] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. These other embodiments are also covered within the scope of protection of this invention.

[0037] Example 1

[0038] This embodiment provides a corn starch-derived hard carbon anode material for sodium-ion batteries, the preparation method of which includes the following steps:

[0039] Raw material preparation: Select 1000 g of corn starch, 50 g of ammonium chloride, and an appropriate amount of deionized water.

[0040] (1) Air oxidation oxidizes the hydroxyl groups on the starch chain to carboxyl groups: Corn starch is placed in an oxidation furnace and air is introduced at a flow rate of 500 mL / min. The oxidation furnace is heated to 240 °C and the air oxidation reaction is carried out at this temperature for 6 h.

[0041] (2) Ammonium chloride-catalyzed esterification and crosslinking of hydroxyl and carboxyl groups in starch: After the air oxidation reaction is completed, the oxidation furnace is cooled to room temperature, the oxidized corn starch is taken out, 50 g of ammonium chloride is added to it and mixed evenly in deionized water. It is dried in a forced-air oven at 50 ℃ to obtain esterified starch.

[0042] (3) Low-temperature carbonization to create open pores: Esterified starch is placed in a carbonization furnace and heated to 600°C under nitrogen atmosphere protection and kept at that temperature for 2 hours. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure.

[0043] (4) High-temperature carbonization to create closed pores: Low-temperature carbonized starch is placed in a carbonization furnace and heated to 1500 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. The carbon layer rearranges and inhibits the growth of microcrystals, so that the open nanopores are transformed into closed pore structures.

[0044] (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery corn starch-derived hard carbon anode material.

[0045] The scanning electron microscope image of the raw corn starch in this embodiment is shown below. Figure 1 As shown, the results indicate that the corn starch is spherical with a relatively small particle size, ranging from 4 to 20 μm. This characteristic may help in the subsequent carbonization process to prepare more uniform hard carbon microspheres. A photograph of the corn starch-derived hard carbon anode material for sodium-ion batteries prepared in this example is shown below. Figure 2 As shown, it appears macroscopically as a black powder with uniform particle size. Its scanning electron microscope image is as follows. Figure 3 As shown, this indicates that the corn starch-derived hard carbon anode material for sodium-ion batteries retains the original spherical morphology of starch, as illustrated in the high-resolution transmission electron microscope image. Figure 4 As shown, the microstructure can be clearly observed to be composed of randomly stacked, curved, short-range ordered graphene sheets. Within these twisted sheet networks, numerous closed pores with a size of approximately 2 nanometers are scattered.

[0046] The biomass-derived hard carbon anode material obtained in this embodiment was used to assemble a battery. The working electrode was prepared according to the ratio of sample: conductive agent acetylene black: polyvinylidene fluoride = 93:2:5. Sodium metal was used as the counter electrode, glass fiber as the separator, and 1M NaPF6 (EC / DEC = 1:1 volume ratio) as the electrolyte. The battery was assembled in a glove box under high-purity argon atmosphere, with a water and oxygen content of less than 0.1 ppm. The half-cell was charged and discharged using a battery tester at current densities ranging from 20 mA / g to 2000 mA / g, with a voltage range of 0.002 V to 3 V.

[0047] The obtained corn starch-derived hard carbon anode material for sodium-ion batteries has a specific surface area of ​​5.5 m². 2 / g, closed-cell volume is 0.2027 cm³. 3 / g. For example... Figure 5 As shown, at a current density of 20 mA / g, the reversible specific capacity is 379.9 mAh / g, and the initial coulombic efficiency is 90%. Figure 6 As shown, at a current density of 100 mA / g, the capacity retention is 99.6% after 100 cycles. Figure 7 As shown, it exhibits excellent rate performance within a current density range of 20-2000 mA / g. Therefore, this demonstrates that the sodium-ion battery anode material prepared using this method possesses ultra-high reversible specific capacity and superior cycle stability compared to previous hard carbon materials. This fully illustrates that the synergistic effect of air oxidation pretreatment and ammonium chloride catalytic pore formation in this invention is crucial for the preparation of high-performance biomass-derived hard carbon anode materials for sodium-ion batteries.

[0048] Compare with Example 1

[0049] This comparative example provides a biomass-derived hard carbon anode material for sodium-ion batteries, and the preparation method is as follows:

[0050] Raw material preparation: 1000 g of corn starch.

[0051] (1) Pretreatment: 1000 g of corn starch was placed in an oxidation furnace and air was introduced at a flow rate of 500 mL / min. The oxidation furnace was heated to 240 °C and heat-treated at this temperature for 6 h.

[0052] (2) Low-temperature carbonization: The pretreated starch is placed in a carbonization furnace and heated to 600 °C under nitrogen atmosphere protection, and kept at that temperature for 2 h.

[0053] (3) High-temperature carbonization: The low-temperature carbonized starch is placed in a carbonization furnace and heated to 1600℃ under nitrogen atmosphere protection, and kept at that temperature for 2 hours.

[0054] (4) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery corn starch-derived hard carbon anode material.

[0055] The only difference between this comparative example and Example 1 is the omission of the key process of ammonium chloride-catalyzed crosslinking and pore formation. This was done to independently evaluate the role of ammonium chloride in stabilizing the precursor structure and forming pores. A photograph of the prepared hard carbon material is shown below. Figure 8 As shown, the material is black overall and has a fluffy, foamy appearance. This is mainly due to insufficient starch dehydration and the rapid escape of a large amount of gas during high-temperature treatment, which destroys the spherical structure. Its scanning electron microscope image is shown below. Figure 9 As shown, the hard carbon material exhibits an irregularly shaped sheet-like structure with a smooth surface, a small number of nanopores, and sharp, irregular edges, failing to maintain the original spherical structure of corn starch. Therefore, starch without ammonium chloride cross-linking and curing leads to the rapid generation and escape of large amounts of gas during high-temperature carbonization, causing the final material to expand and foam. Compared with the results of Example 1, this indicates that the synergistic effect of air oxidation pretreatment and ammonium chloride catalytic pore formation in Example 1 can effectively increase the porosity of the hard carbon material and optimize the closed-pore structure.

[0056] The obtained biomass-derived hard carbon anode material was used to assemble a battery as described in Example 1, and the results showed that the obtained corn starch-derived hard carbon anode material had a specific surface area of ​​41.5 m². 2 / g, closed-cell volume is 0.0730 cm³ 3 / g. At a current density of 20 mA / g, the reversible specific capacity was 300.5 mAh / g, and the initial coulombic efficiency was 78.1%. After 100 cycles at a current density of 100 mA / g, the capacity retention was 90.6%. Although the material obtained in Comparative Example 1 had a higher specific surface area, its closed-cell volume (0.0730 cm³ / g) was much lower than that of Example 1 (0.2027 cm³ / g). Studies have shown that the storage of sodium ions in hard carbon materials mainly depends on closed-cell filling. Due to the lack of the ammonium chloride crosslinking step, Comparative Example 1 had structural instability during high-temperature carbonization, failing to form effective sodium-storing closed pores. At the same time, the excessively high specific surface area led to severe side reactions and irreversible consumption of the SEI film, resulting in significantly lower reversible capacity and initial coulombic efficiency. This conversely demonstrates the crucial role of the ammonium chloride crosslinking step in forming a high-capacity closed-cell structure in this invention.

[0057] Compare with Example 2

[0058] This comparative example provides a corn starch-derived hard carbon anode material for sodium-ion batteries. The preparation method is the same as that provided in Example 1, except that in this comparative example, 1000 g of corn starch is selected, and the amount of ammonium chloride added is 1%, 10% and 40% of the amount of corn starch added, and an appropriate amount of deionized water is added. The above anode materials are numbered a, b and c.

[0059] Scanning electron microscope images of the three sodium-ion battery corn starch-derived hard carbon anode materials prepared in this comparative example are shown below. Figure 10-12 As shown, the results indicate that with the increase of ammonium chloride addition, the adhesion of hard carbon particles is reduced, and a better spherical morphology is maintained. This morphology improvement, combined with the performance data of Examples 11 and 12, shows that the appropriate amount of ammonium chloride is crucial for maintaining the precursor structure and ultimately obtaining excellent electrochemical performance.

[0060] Example 2

[0061] This embodiment provides a potato starch-derived hard carbon anode material for sodium-ion batteries, the preparation method of which includes the following steps:

[0062] Raw material preparation: Select 1000 g potato starch, 50 g ammonium chloride, and an appropriate amount of deionized water.

[0063] (1) Air oxidation to oxidize some of the hydroxyl groups on the potato starch chain to carboxyl groups: Potato starch was placed in an oxidation furnace and air was introduced at a flow rate of 500 mL / min. The oxidation furnace was heated to 240 °C and the air oxidation reaction was carried out at this temperature for 6 h.

[0064] (2) Ammonium chloride-catalyzed esterification and crosslinking of hydroxyl and carboxyl groups in potato starch: After the air oxidation reaction is completed, the oxidation furnace is cooled to room temperature, the oxidized potato starch is taken out, 50 g of ammonium chloride is added to it and deionized water is added and mixed evenly. It is dried in a forced-air drying oven at 50 ℃ to obtain esterified starch.

[0065] (3) Low-temperature carbonization to create open pores: Esterified starch is placed in a carbonization furnace and heated to 600°C under nitrogen atmosphere protection and kept at that temperature for 2 hours. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure.

[0066] (4) High-temperature carbonization to create closed pores: Low-temperature carbonized starch is placed in a carbonization furnace and heated to 1500 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. The carbon layer rearranges and inhibits the growth of microcrystals, so that the open nanopores are transformed into closed pore structures.

[0067] (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery potato starch-derived hard carbon anode material.

[0068] The potato starch-derived hard carbon anode material obtained in this embodiment was used to assemble a battery as described in Example 1, and the results showed that the obtained potato starch-derived hard carbon anode material had a specific surface area of ​​4.5 m². 2 / g, closed-cell volume is 0.1289 cm³. 3 / g. At a current density of 20 mA / g, the reversible specific capacity is 360 mAh / g with an initial coulombic efficiency of 85.7%. At a current density of 100 mA / g, the capacity retention is 99.2% after 100 cycles.

[0069] Example 3

[0070] This embodiment provides a wheat starch-derived hard carbon anode material for sodium-ion batteries, the preparation method of which includes the following steps:

[0071] Raw material preparation: Select 1000 g wheat starch, 50 g ammonium chloride, and an appropriate amount of deionized water.

[0072] (1) Air oxidation to oxidize some of the hydroxyl groups on the wheat starch chain to carboxyl groups: The starch was placed in an oxidation furnace and air was introduced at a flow rate of 500 mL / min. The oxidation furnace was heated to 240 °C and the air oxidation reaction was carried out at this temperature for 6 h.

[0073] (2) Ammonium chloride-catalyzed esterification and crosslinking of hydroxyl and carboxyl groups in wheat starch: After the air oxidation reaction is completed, the oxidation furnace is cooled to room temperature, and 50 g of ammonium chloride and deionized water are added and mixed evenly. The mixture is then dried in a forced-air oven at 50 °C to obtain esterified starch.

[0074] (3) Low-temperature carbonization to create open pores: Esterified starch is placed in a carbonization furnace and heated to 600°C under nitrogen atmosphere protection and kept at that temperature for 2 hours. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure.

[0075] (4) High-temperature carbonization to create closed pores: Low-temperature carbonized starch is placed in a carbonization furnace and heated to 1500 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. The carbon layer rearranges and inhibits the growth of microcrystals, so that the open nanopores are transformed into closed pore structures.

[0076] (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery wheat starch-derived hard carbon anode material.

[0077] The wheat starch-derived hard carbon anode material obtained in this embodiment was used to assemble a battery as described in Example 1, and the results showed that the specific surface area of ​​the obtained wheat starch-derived hard carbon anode material was 4.3 m². 2 / g, closed-cell volume is 0.1356 cm³. 3 / g. At a current density of 20 mA / g, the reversible specific capacity is 363.8 mAh / g, with an initial coulombic efficiency of 86%. At a current density of 100 mA / g, the capacity retention is 99.5% after 100 cycles.

[0078] Example 4

[0079] This embodiment provides a cassava starch-derived hard carbon anode material for sodium-ion batteries, the preparation method of which includes the following steps:

[0080] Raw material preparation: Select 1000 g of cassava starch, 50 g of ammonium chloride, and an appropriate amount of deionized water.

[0081] (1) Air oxidation to oxidize some of the hydroxyl groups on the cassava starch chain to carboxyl groups: The starch was placed in an oxidation furnace and air was introduced at a flow rate of 500 mL / min. The oxidation furnace was heated to 240 °C and the air oxidation reaction was carried out at this temperature for 6 h.

[0082] (2) Ammonium chloride-catalyzed esterification and crosslinking of hydroxyl and carboxyl groups in cassava starch: After the air oxidation reaction is completed, the oxidation furnace is cooled to room temperature, and 50 g of ammonium chloride and deionized water are added and mixed evenly. The mixture is then dried in a forced-air oven at 50 °C to obtain esterified starch.

[0083] (3) Low-temperature carbonization to create open pores: Esterified starch is placed in a carbonization furnace and heated to 600°C under nitrogen atmosphere protection and kept at that temperature for 2 hours. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure.

[0084] (4) High-temperature carbonization to create closed pores: Low-temperature carbonized starch is placed in a carbonization furnace and heated to 1500 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. The carbon layer rearranges and inhibits the growth of microcrystals, so that the open nanopores are transformed into closed pore structures.

[0085] (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery cassava starch-derived hard carbon anode material.

[0086] The obtained cassava starch-derived hard carbon anode material was used to assemble a battery as described in Example 1, and the results showed that the specific surface area of ​​the obtained cassava starch-derived hard carbon anode material was 4.1 m². 2 / g, closed-cell volume is 0.1389 cm³. 3 / g. At a current density of 20 mA / g, the reversible specific capacity is 370.9 mAh / g, with an initial coulombic efficiency of 88.1%. At a current density of 100 mA / g, the capacity retention is 99.3% after 100 cycles.

[0087] Example 5

[0088] This embodiment provides a microcrystalline cellulose-derived hard carbon anode material for sodium-ion batteries, the preparation method of which includes the following steps:

[0089] Raw material preparation: Select 1000 g of microcrystalline cellulose, 50 g of ammonium chloride, and an appropriate amount of deionized water.

[0090] (1) Air oxidation pretreatment: 1000 g of microcrystalline cellulose was placed in an oxidation furnace and air was introduced at a flow rate of 500 mL / min. The oxidation furnace was heated to 240 °C and the air oxidation reaction was carried out at this temperature for 6 h.

[0091] (2) Ammonium chloride-catalyzed esterification: After the air oxidation reaction is completed, the oxidation furnace is cooled to room temperature, and 50 g of ammonium chloride and deionized water are added and mixed evenly. The mixture is then dried in a forced-air oven at 50 °C to obtain esterified microcrystalline cellulose.

[0092] (3) Low-temperature carbonization to create open pores: Esterified microcrystalline cellulose is placed in a carbonization furnace and heated to 600 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure.

[0093] (4) High-temperature carbonization to create closed pores: Low-temperature carbonized microcrystalline cellulose is placed in a carbonization furnace and heated to 1500 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. The carbon layer rearranges and inhibits the growth of microcrystals, so that the open nanopores are transformed into closed pore structures.

[0094] (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery microcrystalline cellulose-derived hard carbon anode material.

[0095] The obtained biomass-derived hard carbon anode material was used to assemble a battery as described in Example 1, and the results showed that the microcrystalline cellulose-derived hard carbon anode material had a specific surface area of ​​0.9 m². 2 / g, closed-cell volume is 0.2472cm³ 3 / g. At a current density of 20 mA / g, the reversible specific capacity is 426.9 mAh / g, with an initial coulombic efficiency of 83.4%. After 100 cycles at a current density of 100 mA / g, the capacity retention is 99.6%.

[0096] Example 6

[0097] This embodiment provides a cellulose-derived hard carbon anode material for sodium-ion batteries, the preparation method of which includes the following steps:

[0098] Raw material preparation: Select 1000 g of cellulose A, 50 g of ammonium chloride, and an appropriate amount of deionized water.

[0099] (1) Air oxidation pretreatment: 1000 g of cellulose A was placed in an oxidation furnace and air was introduced at a flow rate of 500 mL / min. The oxidation furnace was heated to 240 °C and the air oxidation reaction was carried out at this temperature for 6 h.

[0100] (2) Ammonium chloride-catalyzed esterification: After the air oxidation reaction is completed, the oxidation furnace is cooled to room temperature, and 50 g of ammonium chloride and deionized water are added and mixed evenly. The mixture is then dried in a forced-air oven at 50 °C to obtain esterified cellulose methyl ester.

[0101] (3) Low-temperature carbonization to create open pores: Esterified cellulose A is placed in a carbonization furnace and heated to 600 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure.

[0102] (4) High-temperature carbonization to create closed pores: Low-temperature carbonized cellulose A is placed in a carbonization furnace, heated to 1500 ℃ under nitrogen atmosphere protection, and kept at that temperature for 2 h. The carbon layer rearranges, while inhibiting the growth of microcrystals, so that the open nanopores are transformed into closed pore structures.

[0103] (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery cellulose-derived hard carbon anode material.

[0104] The obtained biomass-derived hard carbon anode material was used to assemble a battery, which was then assembled and tested using the method described in Example 1. The results showed that the specific surface area of ​​the cellulose-derived hard carbon anode material was 1.6 m². 2 / g, closed-cell volume is 0.2568 cm³. 3 / g. At a current density of 20 mA / g, the reversible specific capacity is 429.9 mAh / g, with an initial coulombic efficiency of 90.4%. At a current density of 100 mA / g, the capacity retention is 99.9% after 100 cycles.

[0105] Example 7

[0106] This embodiment provides a natural cellulose-derived hard carbon anode material for sodium-ion batteries, the preparation method of which includes the following steps:

[0107] Raw material preparation: Select 1000 g of natural cellulose, 50 g of ammonium chloride, and an appropriate amount of deionized water.

[0108] (1) Air oxidation pretreatment: 1000 g of natural cellulose was placed in an oxidation furnace and air was introduced at a flow rate of 500 mL / min. The oxidation furnace was heated to 240 °C and the air oxidation reaction was carried out at this temperature for 6 h.

[0109] (2) Ammonium chloride-catalyzed esterification: After the air oxidation reaction is completed, the oxidation furnace is cooled to room temperature, and 50 g of ammonium chloride and deionized water are added and mixed evenly. The mixture is then dried in a forced-air oven at 50 °C to obtain esterified natural cellulose.

[0110] (3) Low-temperature carbonization to create open pores: Esterified natural cellulose is placed in a carbonization furnace and heated to 600 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure.

[0111] (4) High-temperature carbonization to create closed pores: Low-temperature carbonized natural cellulose is placed in a carbonization furnace and heated to 1500 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. The carbon layer rearranges and inhibits the growth of microcrystals, so that the open nanopores are transformed into closed pore structures.

[0112] (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery natural cellulose-derived hard carbon anode material.

[0113] The obtained biomass-derived hard carbon anode material was used to assemble a battery as described in Example 1, and the results showed that the specific surface area of ​​the natural cellulose-derived hard carbon anode material was 1.8 m². 2 / g, closed-cell volume is 0.2327cm³ 3 / g. At a current density of 20 mA / g, the reversible specific capacity is 420.9 mAh / g, with an initial coulombic efficiency of 85.1%. After 100 cycles at a current density of 100 mA / g, the capacity retention is 99.5%.

[0114] The "shells" mentioned in this invention include, but are not limited to, common nut shells or kernels such as pine nut shells, macadamia nut shells, and walnut shells, all of which can be effectively converted into high-performance hard carbon materials by the method of this invention.

[0115] Example 8

[0116] This embodiment provides a sodium-ion battery pine nut shell-derived hard carbon anode material, the preparation method of which includes the following steps:

[0117] Raw material preparation: Select 1000 g of pine nut shells, 50 g of ammonium chloride, and an appropriate amount of deionized water.

[0118] (1) Air oxidation pretreatment: 1000 g of pine nut shells were placed in an oxidation furnace and air was introduced at a flow rate of 500 mL / min. The oxidation furnace was heated to 240 °C and the air oxidation reaction was carried out at this temperature for 6 h.

[0119] (2) Ammonium chloride-catalyzed esterification: After the air oxidation reaction is completed, the oxidation furnace is cooled to room temperature, and 50 g of ammonium chloride and deionized water are added and mixed evenly. The mixture is then dried in a forced-air oven at 50 °C to obtain esterified pine nut shells.

[0120] (3) Low-temperature carbonization to create open pores: The esterified pine nut shells are placed in a carbonization furnace and heated to 600℃ under nitrogen atmosphere protection and kept at that temperature for 2 hours. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure.

[0121] (4) High-temperature carbonization to create closed pores: Low-temperature carbonized pine shells are placed in a carbonization furnace and heated to 1500 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. The carbon layers rearrange and the growth of microcrystals is inhibited, so that the open nanopores are transformed into closed pore structures.

[0122] (5) Post-processing: After carbonization, the product is removed, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery pine nut shell-derived hard carbon anode material. Its scanning electron microscope image is shown below. Figure 13 As shown, the microstructure of pine nut shell-derived hard carbon is an irregular rod-shaped structure with a similar particle size distribution, mainly concentrated in the range of 4-6 μm.

[0123] The obtained biomass-derived hard carbon anode material was used to assemble a battery as described in Example 1, and the results showed that the pine nut shell-derived hard carbon anode material had a specific surface area of ​​23 m² at a current density of 20 mA / g. 2 / g, closed-cell volume is 0.1095 cm³ 3 / g. The reversible specific capacity is 340.6 mAh / g, with an initial coulombic efficiency of 84.8%. After 100 cycles at a current density of 100 mA / g, the capacity retention is 99.4%.

[0124] Example 9

[0125] This embodiment provides a hard carbon anode material derived from macadamia nut shells for sodium-ion batteries, the preparation method of which includes the following steps:

[0126] Raw material preparation: 1000 g of macadamia nut shells, 50 g of ammonium chloride, and an appropriate amount of deionized water.

[0127] (1) Air oxidation pretreatment: 1000 g of macadamia nut shells were placed in an oxidation furnace and air was introduced at a flow rate of 500 mL / min. The oxidation furnace was heated to 240 °C and the air oxidation reaction was carried out at this temperature for 6 h.

[0128] (2) Ammonium chloride-catalyzed esterification: After the air oxidation reaction is completed, the oxidation furnace is cooled to room temperature, and 50 g of ammonium chloride and deionized water are added and mixed evenly. The mixture is then dried in a forced-air oven at 50 °C to obtain esterified Hawaiian shells.

[0129] (3) Low-temperature carbonization to create open pores: The esterified Hawaiian shells are placed in a carbonization furnace and heated to 600 °C under nitrogen atmosphere protection and kept at that temperature for 2 h. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure.

[0130] (4) High-temperature carbonization to create closed pores: Low-temperature carbonized macadamia nut shells are placed in a carbonization furnace and heated to 1500 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. The carbon layers rearrange and the growth of microcrystals is inhibited, so that the open nanopores are transformed into closed pore structures.

[0131] (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery macadamia nut shell-derived hard carbon anode material.

[0132] The obtained biomass-derived hard carbon anode material was used to assemble a battery as described in Example 1, and the results showed that the macadamia nut shell-derived hard carbon anode material had a specific surface area of ​​27.2 m². 2 / g, closed-cell volume is 0.1105cm³ 3 / g. At a current density of 20 mA / g, the reversible specific capacity is 345.6 mAh / g, with an initial coulombic efficiency of 85.2%. After 100 cycles at a current density of 100 mA / g, the capacity retention is 99.6%.

[0133] Example 10

[0134] This embodiment provides a walnut shell-derived hard carbon anode material for sodium-ion batteries, the preparation method of which includes the following steps:

[0135] Raw material preparation: Select 1000 g of walnut shells, 50 g of ammonium chloride, and an appropriate amount of deionized water.

[0136] (1) Air oxidation pretreatment: 1000 g of walnut shells were placed in an oxidation furnace and air was introduced at a flow rate of 500 mL / min. The oxidation furnace was heated to 240 °C and the air oxidation reaction was carried out at this temperature for 6 h.

[0137] (2) Ammonium chloride-catalyzed esterification: After the air oxidation reaction is completed, the oxidation furnace is cooled to room temperature, and 50 g of ammonium chloride and deionized water are added and mixed evenly. The mixture is then dried in a forced-air oven at 50 °C to obtain esterified walnut shells.

[0138] (3) Low-temperature carbonization to create open pores: The esterified walnut shells are placed in a carbonization furnace and heated to 600°C under nitrogen atmosphere protection and kept at that temperature for 2 hours. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure.

[0139] (4) High-temperature carbonization to create closed pores: Low-temperature carbonized walnut shells are placed in a carbonization furnace and heated to 1500 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. The carbon layers rearrange and microcrystal growth is inhibited, so that the open nanopores are transformed into closed pore structures.

[0140] (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery walnut shell-derived hard carbon anode material.

[0141] The obtained biomass-derived hard carbon anode material was used to assemble batteries as described in Example 1, and the results showed that the walnut shell-derived hard carbon anode material had a specific surface area of ​​16 m². 2 / g, closed-cell volume is 0.1465 cm³. 3 / g. At a current density of 20 mA / g, the reversible specific capacity is 358.6 mAh / g, with an initial coulombic efficiency of 85.6%. At a current density of 100 mA / g, the capacity retention is 99.6% after 100 cycles.

[0142] Example 11

[0143] This embodiment provides a corn starch-derived hard carbon anode material for sodium-ion batteries, the preparation method of which includes the following steps:

[0144] Raw material preparation: Select 1000 g of corn starch, 1 g of ammonium chloride, and an appropriate amount of deionized water.

[0145] (1) Air oxidation pretreatment: 1000 g of corn starch was placed in an oxidation furnace and air was introduced at a flow rate of 500 mL / min. The oxidation furnace was heated to 240 °C and the air oxidation reaction was carried out at this temperature for 6 h.

[0146] (2) Ammonium chloride-catalyzed esterification: After the air oxidation reaction is completed, the oxidation furnace is cooled to room temperature, 1 g of ammonium chloride is added and deionized water is added and mixed evenly. The mixture is then dried in a forced-air oven at 50 °C to obtain esterified corn starch.

[0147] (3) Low-temperature carbonization to create open pores: Esterified starch is placed in a carbonization furnace and heated to 600°C under nitrogen atmosphere protection and kept at that temperature for 2 hours. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure.

[0148] (4) High-temperature carbonization to create closed pores: Low-temperature carbonized starch is placed in a carbonization furnace and heated to 1500 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. The carbon layer rearranges and inhibits the growth of microcrystals, so that the open nanopores are transformed into closed pore structures.

[0149] (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery corn starch-derived hard carbon anode material.

[0150] The obtained biomass-derived hard carbon anode material was used to assemble a battery as described in Example 1, and the results showed that the obtained corn starch-derived hard carbon anode material had a specific surface area of ​​9.6 m². 2 / g, closed-cell volume is 0.0802 cm³ 3 / g. At a current density of 20 mA / g, the reversible specific capacity is 311.6 mAh / g, with an initial coulombic efficiency of 80.1%. At a current density of 100 mA / g, the capacity retention is 95.2% after 100 cycles.

[0151] Example 12

[0152] This embodiment provides a corn starch-derived hard carbon anode material for sodium-ion batteries, the preparation method of which includes the following steps:

[0153] Raw material preparation: Select 1000 g of corn starch, 1000 g of ammonium chloride, and an appropriate amount of deionized water.

[0154] (1) Air oxidation pretreatment: 1000 g of corn starch was placed in an oxidation furnace and air was introduced at a flow rate of 500 mL / min. The oxidation furnace was heated to 240 °C and the air oxidation reaction was carried out at this temperature for 6 h.

[0155] (2) Ammonium chloride-catalyzed esterification: After the air oxidation reaction is completed, the oxidation furnace is cooled to room temperature, and 1000 g of ammonium chloride and deionized water are added and mixed evenly. The mixture is then dried in a forced-air oven at 50 °C to obtain esterified corn starch.

[0156] (3) Low-temperature carbonization to create open pores: Esterified starch is placed in a carbonization furnace and heated to 600°C under nitrogen atmosphere protection and kept at that temperature for 2 hours. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure.

[0157] (4) High-temperature carbonization to create closed pores: Low-temperature carbonized starch is placed in a carbonization furnace and heated to 1500 ℃ under nitrogen atmosphere protection and kept at that temperature for 2 h. The carbon layer rearranges and inhibits the growth of microcrystals, so that the open nanopores are transformed into closed pore structures.

[0158] (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery corn starch-derived hard carbon anode material.

[0159] The obtained biomass-derived hard carbon anode material was used to assemble a battery as described in Example 1, and the results showed that the specific surface area of ​​the obtained corn starch-derived hard carbon anode material was 8.1 m². 2 / g, closed-cell volume is 0.0859 cm³. 3 / g. At a current density of 20 mA / g, the reversible specific capacity is 320.4 mAh / g, and the initial coulombic efficiency is 80.2%. After 100 cycles at a current density of 100 mA / g, the capacity retention is 93.2%. Both excessively high and low ammonium chloride ratios lead to performance degradation, indicating that the amount of ammonium chloride has a non-linear effect on performance. Therefore, even when the amount of ammonium chloride deviates from the optimal ratio, the resulting crosslinking and pore-forming effects still significantly improve the material's structural performance compared to Control Example 1, which did not use any ammonium chloride, demonstrating the core advantages of the method of this invention.

[0160] This invention also provides parallel experiments of Example 1, using the same preparation method as Example 1 to prepare corn starch-derived hard carbon anode materials, which are named Examples 13-19. The preparation data and electrochemical data of the products are shown in Table 1:

[0161] Table 1. Preparation data and electrochemical performance test results of Examples 13-19

[0162]

[0163] Note: Except for the above-mentioned variable parameters, the other preparation conditions are the same as in Example 1, namely, 1000 g of corn starch, air oxidation time of 6 h, drying temperature of 50 ℃, etc.

[0164] Therefore, this invention discloses a biomass-derived hard carbon anode material for sodium-ion batteries and its preparation method and application based on cross-linking pore formation. This method can improve the porosity of the hard carbon material, optimize the closed-pore structure, and improve the sodium ion transport and storage efficiency, giving the material advantages such as high specific capacity, high initial coulombic efficiency, high rate performance, and high energy density. Moreover, the process is simple, low-cost, and environmentally friendly, solving the problems of low porosity and insufficient electrochemical performance of traditional hard carbon materials in existing sodium-ion battery anode materials.

[0165] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and does not limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a biomass-derived hard carbon anode material for sodium-ion batteries based on cross-linking pore formation, characterized in that, Includes the following steps: Step (1) Air oxidation oxidizes the hydroxyl groups on the biomass chain to carboxyl groups: Place the biomass material in an oxidation furnace and continuously introduce air at a flow rate of 100-5000 mL / min; raise the temperature to 150-350 ℃ and keep it at that temperature for 1-20 h; Step (2) Ammonium chloride catalyzes the esterification and crosslinking of hydroxyl and carboxyl groups in biomass: The oxidized biomass material is mixed with ammonium chloride in deionized water and stirred evenly, and then dried at a temperature of 35-160 °C to obtain esterified biomass material; In step (2), the mass ratio of biomass material to ammonium chloride is 1:(0.001-1). Step (3) Low-temperature carbonization to create open pores: The esterified biomass material is placed in a carbonization furnace and heated to 500-900 ℃ under inert gas protection and kept at that temperature for 1-4 h. Ammonium chloride decomposes to produce NH3 and HCl gas, and the gas escapes to form an open nanoporous structure. Step (4) High-temperature carbonization to create closed pores: The biomass material after low-temperature carbonization is placed in a carbonization furnace, and under the protection of inert gas, the temperature is raised to 1100-1600 ℃ and kept for 1-4 h to promote the transformation of open nanopore structure into closed pore structure. Step (5) Post-processing: After carbonization, the product is taken out, washed with deionized water until neutral, and dried to obtain the final sodium-ion battery biomass-derived hard carbon anode material.

2. The method for preparing a sodium-ion battery biomass-derived hard carbon anode material based on cross-linking pore formation according to claim 1, characterized in that, In step (1), the biomass is selected from one or more of potato starch, corn starch, wheat starch, cassava starch, natural cellulose, microcrystalline cellulose, methyl cellulose, and fruit shells.

3. A biomass-derived hard carbon anode material for sodium-ion batteries, characterized in that, The sodium-ion battery biomass-derived hard carbon anode material is prepared by the preparation method according to any one of claims 1-2, wherein the sodium-ion battery biomass-derived hard carbon anode material has nanopores containing closed-pore structures.

4. An application of the sodium-ion battery biomass-derived hard carbon anode material as described in claim 3, characterized in that, The aforementioned sodium-ion battery biomass-derived hard carbon anode material is used in sodium-ion battery hard carbon anode materials.

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