High-yield sodium ion battery biomass hard carbon negative electrode material and preparation method thereof

Abstract

The invention discloses a high-yield sodium ion battery biomass hard carbon negative electrode material and a preparation method thereof.The preparation method comprises the steps that S1, pretreatment is conducted, specifically, a biomass raw material is crushed and sieved, and a refined precursor is obtained; s2, activating treatment: performing activating treatment on the refined precursor obtained in the step S1 by adopting an acid solution, and performing drying treatment to obtain an activated precursor; s3, cross-linking treatment: ball-milling and uniformly mixing the activated precursor obtained in the step S2 and a cross-linking agent to obtain a composite precursor; s4, oxidation treatment: carrying out oxidation treatment on the composite precursor obtained in the step S3 in an oxidation atmosphere to obtain an oxidized precursor; and S5, high-temperature carbonization: performing high-temperature carbonization on the oxidized precursor obtained in the step S4 to obtain the final hard carbon negative electrode material. The high-yield sodium ion battery biomass hard carbon negative electrode material and the preparation method thereof have the characteristics of high product yield, high reversible capacity and low cost.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a high-yield sodium-ion battery biomass hard carbon anode material and its preparation method. Background Technology

[0002] With the continuous growth of global energy demand and the increasing severity of environmental problems, research on sustainable energy technologies is of paramount importance. Among these, sodium-ion batteries, with their core advantages of high safety, environmental friendliness, and low cost, have demonstrated enormous application potential in areas such as large-scale energy storage, low-speed electric vehicles, and smart home energy storage. This system, combined with low-cost anode materials such as hard carbon, not only reduces device fabrication costs but also possesses excellent low-temperature performance, rate capability, and cycle stability. This effectively compensates for the shortcomings of lithium-ion batteries in terms of resource constraints and cost control, providing a reliable energy storage solution for the large-scale grid connection of renewable energy.

[0003] Although hard carbon materials are the core choice for anodes in sodium-ion batteries, their practical application still faces multiple obstacles. The core problem of low capacity directly restricts the further marketization and technological breakthroughs of sodium-ion batteries.

[0004] In addition, the low yield of hard carbon materials is also a prominent issue. This shortcoming not only limits its large-scale production efficiency, but also further restricts the development and industrialization of sodium-ion batteries.

[0005] Currently, pre-oxidation technology is widely used in the industry to improve the specific capacity of hard carbon. Pre-oxidation is a key step in the hard carbon preparation process, connecting precursor pretreatment and high-temperature carbonization. Specifically, it involves controlled oxidation of precursors such as biomass (coconut shells, straw), polymers (polypyrrole, sucrose), or coal by-products in a mild temperature range of 200-400℃ using an oxidizing atmosphere such as oxygen or ozone.

[0006] During this process, oxidation selectively breaks some weak bonds such as CH and CC within the precursor, removing some volatile components such as hydrogen and oxygen. On one hand, this promotes the formation of micropores adapted for sodium ion transport on the surface and inside the precursor, further increasing the specific surface area to increase sodium storage contact sites; on the other hand, it introduces a large number of edge defects into the carbon framework. These newly formed pores can store sodium ions through a "micropore filling" mechanism, while structural defects can provide additional "surface adsorption" sodium storage sites. The synergistic effect of these two factors significantly improves the reversible specific capacity of hard carbon.

[0007] While pre-oxidation methods offer advantages such as low processing costs and significant capacity improvements, they still face several practical bottlenecks in application. One key factor is that the capacity improvement from pre-oxidation is closely related to the precursor's structure. The inherent molecular chain structure and elemental composition of the precursor limit the potential for oxidation modification. Once porosity and defect density reach a certain threshold, further oxidation can easily lead to carbon framework collapse, resulting in a decrease in capacity. Therefore, simply extending the oxidation time or increasing the oxidation temperature cannot overcome the capacity bottleneck, and further capacity improvements are difficult to achieve.

[0008] Meanwhile, during the oxidation process, while volatiles such as hydrogen and oxygen in the precursor are removed, some carbon elements are also oxidized and lost, resulting in a significant reduction in the yield of subsequent carbonization, which in turn increases the production cost per unit of material and ultimately indirectly weakens the overall cost advantage of sodium-ion batteries. Summary of the Invention

[0009] The purpose of this invention is to provide a high-yield sodium-ion battery biomass hard carbon anode material and its preparation method, which features high product yield, high reversible capacity and low cost.

[0010] This invention can be achieved through the following technical solutions:

[0011] The present invention discloses a high-yield method for preparing biomass hard carbon anode material for sodium-ion batteries, comprising the following steps:

[0012] S1. Pretreatment: The biomass raw material is crushed and sieved to obtain a refined precursor;

[0013] S2. Activation treatment: The refined precursor obtained in step S1 is activated with an acidic solution and then dried to obtain the activated precursor.

[0014] S3. Crosslinking treatment: The activated precursor obtained in step S2 is ball-milled and mixed with the crosslinking agent to obtain a composite precursor.

[0015] S4. Oxidation treatment: The composite precursor obtained in step S3 is oxidized in an oxidizing atmosphere to obtain an oxidized precursor.

[0016] S5. High-temperature carbonization: The oxide precursor obtained in step S4 is subjected to high-temperature carbonization to obtain the final hard carbon anode material.

[0017] Further, in step S2, the acidic solution is one or more of sulfuric acid, hydrochloric acid, nitric acid, boric acid, citric acid, oxalic acid, phytic acid, formic acid, propionic acid, acetic acid, and perchloric acid. The concentration of the acidic solution is 0.5-2 mol / L, the activation temperature is 80-120℃, and the activation time is 3-8 h. In this invention, the role of the acidic solution is to disrupt the hydrogen bond network between lignin, cellulose, and hemicellulose within the precursor through acid catalysis and selective degradation, while simultaneously breaking some weak ether bonds (such as aryl ether bonds in lignin and glycosidic bonds in cellulose). This process not only loosens the dense three-dimensional network structure of the precursor but also fully exposes the active groups (such as cellulose hydroxyl groups, lignin phenolic hydroxyl groups, and hemicellulose carboxyl groups) that were originally encapsulated inside. In addition, the moderate etching of the acidic solution can form micropores and channels on the surface and inside of the material, further increasing the number of binding sites between the crosslinking agent and the precursor, while avoiding insufficient local crosslinking, thus laying a structural foundation for subsequent uniform and efficient crosslinking reactions. Specifically, if the acid solution concentration is too high, the reaction temperature is too high, or the reaction time is too long, the hydrogen bond network of the precursor is completely broken down. Simultaneously, a large number of weak ether bonds (aryl ether bonds, glycosidic bonds) and even some strong chemical bonds break. This causes the original skeletal structure of the precursor to collapse, making it impossible to maintain a stable three-dimensional structure. Consequently, subsequent cross-linking reactions lose a reliable structural base, making it difficult to form a uniform and effective cross-linking network. If the acid solution concentration is too low, the reaction temperature is too low, or the reaction time is too short, the degree of damage to the hydrogen bond network of the precursor is limited. The binding forces between lignin, cellulose, and hemicellulose are not significantly weakened, and the dense three-dimensional network structure of the precursor is difficult to effectively loosen, failing to create conditions for subsequent cross-linking reactions.

[0018] Further, in step S3, the crosslinking agent is one or more of asphalt, resin, and carbohydrate compounds. The role of the crosslinking agent is to chemically react with the active groups such as hydroxyl, carboxyl, and phenolic hydroxyl groups exposed on the surface of the precursor through its own oxygen-containing functional groups (such as hydroxyl, epoxy, and carbonyl groups), nitrogen-containing / sulfur-containing functional groups (such as amino, isocyanate, and thioether groups), or unsaturated hydrocarbon groups (such as double and triple bonds), to construct stable covalent chemical bonds (such as ester bonds, ether bonds, amide bonds, CN bonds, and CS bonds), enabling the precursor to form a stable carbon skeleton structure during carbonization. This stable skeleton structure, on the one hand, fixes hydrogen and oxygen atoms in the network structure through strong covalent bonds, thereby reducing the generation and loss of volatile pyrolysis products such as methane and carbon monoxide, and reducing material loss; on the other hand, it prevents the precursor structure from collapsing during oxidation, maintains the integrity of pores and channels, ensures uniform oxygen penetration, and avoids waste from localized excessive oxidation and ablation. Ultimately, this significantly increases the overall yield of the oxidation reaction. Furthermore, the crosslinking agent molecules interpenetrate and crosslink between the precursor molecular chains, forming numerous tiny gaps between the chains. These gaps, after carbonization, transform into a rich microporous structure, providing more storage sites for sodium ions and further enhancing capacity. Simultaneously, the stable carbon framework structure formed after precursor crosslinking effectively suppresses excessive graphitization of the carbon layers, maintaining the interlayer spacing within the optimal range of 0.37–0.40 nm, thus meeting the sodium ion intercalation requirements and significantly improving interlayer sodium storage capacity, further driving capacity growth.

[0019] Furthermore, in step S3, the amount of crosslinking agent added is 1-8% of the precursor mass. If too much crosslinking agent is added, it will cause the crosslinking agent and the precursor to form an overly dense crosslinking network, hindering oxygen penetration and preventing effective oxidation inside the precursor, resulting in capacity loss. Excessive crosslinking agent may also clog existing pores, leading to a significant reduction in sodium ion storage sites, ultimately causing a decrease in hard carbon capacity instead of an increase. If too little crosslinking agent is added, it can only react with a small number of active groups on the precursor surface, failing to construct a complete three-dimensional covalent network. This makes it difficult for the precursor to form a stable carbon skeleton structure during oxidation, making it difficult to fix hydrogen and oxygen atoms in the network structure through strong covalent bonds. This results in a significant loss of volatile pyrolysis products such as methane and carbon monoxide, ultimately failing to improve the pre-oxidation yield. Simultaneously, a small amount of crosslinking agent cannot fully penetrate between the precursor molecular chains, resulting in insufficient inter-chain pores, a scarcity of microporous structures after carbonization, and a lack of sodium ion storage sites, preventing an effective increase in hard carbon capacity.

[0020] Further, in step S4, the oxidation temperature is 200-400℃, the oxidation time is 2-8h, and the oxidation atmosphere is air and / or ozone. If the oxidation temperature is too high or the oxidation time is too long, it will cause over-oxidation or even local ablation of the precursor, leading to increased material loss and decreased yield. In addition, over-oxidation will destroy the originally ordered or graphite-like local structure, thereby forming a large number of defects and macroporous structures, resulting in poor hard carbon cycling performance. If the oxidation temperature is too low or the oxidation time is too short, the active groups of the precursor cannot be effectively converted into oxygen-containing functional groups, resulting in insufficient and uneven oxidation of the precursor, and ultimately the sodium storage capacity of the hard carbon will not reach the expected level. In the oxidation process of this invention, the weak bonds such as CH and CC inside the precursor undergo selective breakage. Under the action of the crosslinking agent, this process effectively retains the carbon component while orderly removing volatile components such as hydrogen and oxygen, thereby forming micropores adapted to sodium ion transport on the surface and inside of the precursor. This not only expands the specific surface area of ​​the material and increases the number of sodium storage contact sites, but also allows the tiny inter-chain gaps formed by the crosslinking agent molecules to be retained and expanded during the breaking of weak bonds and the release of volatile substances, becoming an important source of more microporous structures. Simultaneously, the stable carbon framework formed by crosslinking effectively maintains the integrity of the pore channels, ensuring uniform oxygen permeation during oxidation. This avoids the yield reduction caused by localized excessive oxidation and ablation, and also allows for the uniform introduction of a large number of edge defects into the carbon framework. The new pores generated during oxidation can store sodium ions through a "micropore filling" mechanism, while structural defects provide additional sodium storage sites through a "surface adsorption" mechanism. The synergistic effect of these two mechanisms significantly improves the reversible specific capacity of hard carbon materials. Furthermore, the stable carbon framework structure constructed by crosslinking effectively suppresses excessive graphitization of the carbon layers, stabilizing the interlayer spacing within the optimal range of 0.37–0.40 nm. This structural characteristic better adapts to the sodium ion embedding requirements, thereby significantly improving the interlayer sodium storage capacity and further promoting the overall capacity improvement of the material.

[0021] Furthermore, in step S5, the conditions for high-temperature carbonization are: a heating rate of 1-5℃ / min, a carbonization temperature of 1200-1600℃, and a carbonization time of 2-10 h.

[0022] Furthermore, in step S1, the biomass raw material is one or more of the following: walnut shells, chestnut shells, peanut shells, coconut shells, almond shells, camellia shells, corn cobs, sugarcane bagasse, wood chips, bamboo chips, corn stalks, wheat stalks, rice stalks, and cotton stalks.

[0023] Another aspect of the present invention is to protect a sodium-ion battery biomass hard carbon anode material, which is prepared by the above-described preparation method.

[0024] This invention discloses a high-yield biomass hard carbon anode material for sodium-ion batteries and its preparation method, which has the following beneficial effects:

[0025] First, the product yield is high. The preparation method of this invention, with the assistance of a crosslinking agent, effectively improves the problem of large carbon skeleton loss in traditional oxidation processes. The three-dimensional network constructed by the crosslinking agent can enhance the stability of the precursor carbon backbone, enabling the selective breaking of weak bonds such as CH and CC during oxidation. This allows for the orderly removal of non-carbon components such as hydrogen and oxygen while maximizing the retention of the carbon matrix. In addition, the stable framework formed after crosslinking can maintain the integrity of the pore channels, ensuring uniform oxygen penetration during oxidation and avoiding material ablation and carbon loss caused by severe oxidation and ablation due to localized heat accumulation, thereby improving the overall yield of the material.

[0026] Secondly, the material exhibits high reversible capacity. In the preparation method described in this invention, crosslinking and oxidation processes synergistically regulate the microstructural evolution of the carbon material. During oxidation, the introduced crosslinking agent enables selective bond breaking of the precursor under the constraint of the crosslinking network, promoting the orderly removal of volatile components and thus constructing a microporous structure conducive to sodium ion transport. Simultaneously, the presence of the crosslinked framework effectively maintains the micropores between chains and allows for further expansion of these pores during the oxidation stage, thereby enriching the microporous system of the material. Furthermore, the stable crosslinked framework allows oxygen to permeate uniformly into the material, enabling the uniform formation of edge defects within the carbon framework, thus providing more additional sodium storage sites. In addition, the crosslinked structure effectively constrains the carbon framework, inhibiting excessive graphitization of the carbon layers during oxidation and stabilizing the interlayer spacing within the optimal range of 0.37–0.40 nm, significantly facilitating the reversible insertion and extraction of sodium ions and improving the interlayer sodium storage capacity. Therefore, the synergistic effect of crosslinking regulation, oxidation etching, and structural stability significantly enhances the reversible sodium storage capacity of the material.

[0027] Third, the cost is low. Compared with the prior art, the preparation method of this invention optimizes the activation, cross-linking, and oxidation processes, and can be carried out in a reaction vessel, which is convenient for industrialization and effectively simplifies the preparation process. Thus, the cost is effectively reduced while ensuring the yield and electrochemical performance. Attached Figure Description

[0028] Figure 1 The first-week charge-discharge curve of Application Example 1;

[0029] Figure 2 The first-week charge-discharge curves for application Example 2;

[0030] Figure 3 The first-week charge-discharge curve for Comparative Example 1

[0031] Figure 4 The first-week charge-discharge curves are for Comparative Example 2. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0033] The present invention discloses a high-yield method for preparing biomass hard carbon anode material for sodium-ion batteries, comprising the following steps:

[0034] S1. Pretreatment: The biomass raw material is crushed and sieved to obtain a refined precursor;

[0035] S2. Activation treatment: The refined precursor obtained in step S1 is activated by an acidic solution and then dried to obtain the activated precursor.

[0036] S3. Crosslinking treatment: The activated precursor obtained in step S2 is ball-milled and mixed with the crosslinking agent to obtain a composite precursor.

[0037] S4. Oxidation treatment: The composite precursor obtained in step S3 is oxidized in an oxidizing atmosphere to obtain an oxidized precursor.

[0038] S5. High-temperature carbonization: The oxide precursor obtained in step S4 is subjected to high-temperature carbonization to obtain the final hard carbon anode material.

[0039] Further, in step S2, the acidic solution is one or more of sulfuric acid, hydrochloric acid, nitric acid, boric acid, citric acid, oxalic acid, phytic acid, formic acid, propionic acid, acetic acid, and perchloric acid, the concentration of the acidic solution is 0.5-2 mol / L, the activation temperature is 80-120℃, and the activation time is 3-8 h.

[0040] Furthermore, in step S3, the crosslinking agent is one or more of asphalt, resin, and carbohydrate compounds.

[0041] Furthermore, in step S3, the amount of crosslinking agent added is 1-8% of the precursor mass.

[0042] Furthermore, in step S4, the oxidation temperature is 200-400℃, the oxidation time is 2-8h, and the oxidation atmosphere is air and / or ozone.

[0043] Furthermore, in step S5, the conditions for high-temperature carbonization are: a heating rate of 1-5℃ / min, a carbonization temperature of 1200-1600℃, and a carbonization time of 2-10 h.

[0044] Furthermore, in step S1, the biomass raw material is one or more of the following: walnut shells, chestnut shells, peanut shells, coconut shells, almond shells, camellia shells, corn cobs, sugarcane bagasse, wood chips, bamboo chips, corn stalks, wheat stalks, rice stalks, and cotton stalks.

[0045] Another aspect of the present invention is to protect a sodium-ion battery biomass hard carbon anode material, which is prepared by the above-described preparation method.

[0046] Example 1

[0047] This embodiment relates to a biomass hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:

[0048] S1. Pretreatment: The biomass raw materials are crushed and sieved to obtain refined precursors. Specifically, the biomass raw materials are walnut shells, chestnut shells, and cotton stalks.

[0049] S2. Activation treatment: The refined precursor obtained in step S1 is activated using an acidic solution and then dried to obtain the activated precursor. Specifically, the acidic solution is sulfuric acid or hydrochloric acid, the concentration of the acidic solution is 2 mol / L, the activation temperature is 100℃, and the activation time is 3 h.

[0050] S3. Crosslinking treatment: The activated precursor obtained in step S2 is ball-milled and mixed evenly with the crosslinking agent to obtain a composite precursor. Specifically, the crosslinking agent is asphalt, and the amount of crosslinking agent added is 8% of the precursor mass.

[0051] S4. Oxidation treatment: The composite precursor obtained in step S3 is oxidized in an oxidizing atmosphere to obtain an oxidized precursor. Specifically, the oxidation temperature is 400℃, the oxidation time is 5 hours, and the oxidizing atmosphere is air.

[0052] S5. High-temperature carbonization: The oxide precursor obtained in step S4 is subjected to high-temperature carbonization to obtain the final hard carbon anode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 5℃ / min, carbonization temperature of 1400℃, and carbonization time of 2h.

[0053] Example 2

[0054] This embodiment relates to a biomass hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:

[0055] S1. Pretreatment: The biomass raw materials are crushed and sieved to obtain refined precursors. Specifically, the biomass raw materials are almond shells, camellia shells, corn cobs, sugarcane bagasse, and wood chips.

[0056] S2. Activation treatment: The refined precursor obtained in step S1 is activated using an acidic solution and then dried to obtain the activated precursor. Specifically, the acidic solution is sulfuric acid, oxalic acid, phytic acid, formic acid, or propionic acid, with a concentration of 1.2 mol / L. The activation temperature is 80℃, and the activation time is 8 hours.

[0057] S3. Crosslinking treatment: The activated precursor obtained in step S2 is ball-milled and mixed evenly with the crosslinking agent to obtain a composite precursor. Specifically, the crosslinking agent is a resin, and the amount of crosslinking agent added is 4% of the precursor mass.

[0058] S4. Oxidation treatment: The composite precursor obtained in step S3 is oxidized in an oxidizing atmosphere to obtain an oxidized precursor. Specifically, the oxidation temperature is 300℃, the oxidation time is 2 hours, and the oxidizing atmosphere is ozone.

[0059] S5. High-temperature carbonization: The oxide precursor obtained in step S4 is subjected to high-temperature carbonization to obtain the final hard carbon anode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 3℃ / min, carbonization temperature of 1200℃, and carbonization time of 10 h.

[0060] Example 3

[0061] This embodiment relates to a biomass hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:

[0062] S1. Pretreatment: The biomass raw materials are crushed and sieved to obtain refined precursors. Specifically, the biomass raw materials are camellia oleifera shells, corn cobs, sugarcane bagasse, wood chips, bamboo chips, and corn stalks.

[0063] S2. Activation treatment: The refined precursor obtained in step S1 is activated using an acidic solution and then dried to obtain the activated precursor. Specifically, the acidic solution is sulfuric acid, boric acid, citric acid, or acetic acid, with a concentration of 0.5 mol / L, an activation temperature of 120℃, and an activation time of 5 h.

[0064] S3. Crosslinking treatment: The activated precursor obtained in step S2 is ball-milled and mixed evenly with the crosslinking agent to obtain a composite precursor. Specifically, the crosslinking agent is a carbohydrate compound, and the amount of crosslinking agent added is 2% of the precursor mass.

[0065] S4. Oxidation treatment: The composite precursor obtained in step S3 is oxidized in an oxidizing atmosphere to obtain an oxidized precursor. Specifically, the oxidation temperature is 200℃, the oxidation time is 8 hours, and the oxidizing atmosphere is ozone.

[0066] S5. High-temperature carbonization: The oxide precursor obtained in step S4 is subjected to high-temperature carbonization to obtain the final hard carbon anode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 1℃ / min, carbonization temperature of 1600℃, and carbonization time of 6 h.

[0067] Example 4

[0068] This embodiment relates to a biomass hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:

[0069] S1. Pretreatment: The biomass raw materials are crushed and sieved to obtain refined precursors. Specifically, the biomass raw materials are walnut shells, chestnut shells, peanut shells, coconut shells, almond shells, rice straw, and cotton straw.

[0070] S2. Activation treatment: The refined precursor obtained in step S1 is activated using an acidic solution and then dried to obtain the activated precursor. Specifically, the acidic solution is citric acid, oxalic acid, acetic acid, or perchloric acid, with a concentration of 1 mol / L, an activation temperature of 90℃, and an activation time of 4 h.

[0071] S3. Crosslinking treatment: The activated precursor obtained in step S2 is ball-milled and mixed evenly with the crosslinking agent to obtain a composite precursor. Specifically, the crosslinking agent is asphalt or a carbohydrate compound, and the amount of crosslinking agent added is 3% of the precursor mass.

[0072] S4. Oxidation treatment: The composite precursor obtained in step S3 is oxidized in an oxidizing atmosphere to obtain an oxidized precursor. Specifically, the oxidation temperature is 250℃, the oxidation time is 6 hours, and the oxidizing atmosphere is air and ozone.

[0073] S5. High-temperature carbonization: The oxide precursor obtained in step S4 is subjected to high-temperature carbonization to obtain the final hard carbon anode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 2℃ / min, carbonization temperature of 1500℃, and carbonization time of 8 h.

[0074] Example 5

[0075] This embodiment relates to a biomass hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:

[0076] S1. Pretreatment: The biomass raw materials are crushed and sieved to obtain refined precursors. Specifically, the biomass raw materials are walnut shells, chestnut shells, peanut shells, coconut shells, and almond shells.

[0077] S2. Activation treatment: The refined precursor obtained in step S1 is activated using an acidic solution and then dried to obtain the activated precursor. Specifically, the acidic solution is sulfuric acid, hydrochloric acid, acetic acid, or perchloric acid, the concentration of the acidic solution is 1.3 mol / L, the activation temperature is 110℃, and the activation time is 7 h.

[0078] S3. Crosslinking treatment: The activated precursor obtained in step S2 is ball-milled and mixed evenly with the crosslinking agent to obtain a composite precursor. Specifically, the crosslinking agent is asphalt, resin, or a sugar compound, and the amount of crosslinking agent added is 6% of the precursor mass.

[0079] S4. Oxidation treatment: The composite precursor obtained in step S3 is oxidized in an oxidizing atmosphere to obtain an oxidized precursor. Specifically, the oxidation temperature is 350℃, the oxidation time is 4 hours, and the oxidizing atmosphere is air and ozone.

[0080] S5. High-temperature carbonization: The oxide precursor obtained in step S4 is subjected to high-temperature carbonization to obtain the final hard carbon anode material. Specifically, the conditions for high-temperature carbonization are: heating rate of 4℃ / min, carbonization temperature of 13600℃, and carbonization time of 4 h.

[0081] Application Example 1

[0082] This embodiment relates to a biomass hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:

[0083] S1. Pretreatment: Preparation of biomass hard carbon materials: Crush bamboo raw materials and sieve them through a 60-mesh sieve to obtain bamboo powder raw materials.

[0084] S2. Activation treatment: The bamboo powder obtained by sieving in step S1 is placed in a reaction vessel, a 1 mol / L sulfuric acid solution is added, and the mixture is heated to 90°C and reacted for 6 hours. Subsequently, it is dried at 80°C for 12 hours to obtain activated bamboo powder.

[0085] S3. Crosslinking treatment: The activated bamboo powder obtained in step S2 and phenolic resin are placed in a ball mill jar and ball-milled and mixed evenly. The amount of phenolic resin added is 4% of the mass of bamboo powder, and composite bamboo powder is obtained.

[0086] S4. Oxidation treatment: The composite bamboo powder obtained in step S3 is oxidized in an oxygen atmosphere at 220°C for 4 hours to obtain oxidized bamboo powder.

[0087] S5. High-temperature carbonization: The oxidized bamboo powder obtained in step S4 is heated to 800°C at 5°C / min under a nitrogen atmosphere, and then heated to 1300°C at 2°C / min and held for 2 hours to obtain the final hard carbon finished material.

[0088] The electrochemical performance of the obtained materials was tested as follows: Hard carbon material, Super P, CMC, and SBR were mixed in a mass ratio of 94:1.5:2:2.5 to form a slurry. A 60 μm four-sided coating tool was used to coat the black slurry onto copper foil, and the membrane was then dried in a vacuum oven at 100°C for 2 hours. The electrode membrane was punched into 12 mm diameter discs using a die-cutting machine. Using metallic sodium as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) as the electrolyte, and a PP double-layer separator, CR2032 type button cells were assembled in a glove box. Constant current charge-discharge tests were performed on the above button cells at a current density of 0.1C (1C = 300 mAh / g) and a voltage range of 2–0.005 V.

[0089] Application Example 2

[0090] This embodiment relates to a biomass hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:

[0091] S1. Pretreatment: Preparation of biomass hard carbon materials: Crush almond shells and sieve through a 60-mesh sieve to obtain apricot powder raw material.

[0092] S2. Activation treatment: The apricot powder obtained by sieving in step S1 is placed in a reaction vessel, and a sulfuric acid solution with a concentration of 0.5 mol / L is added. The mixture is heated to 100°C and reacted for 4 hours. Subsequently, it is dried at 80°C for 12 hours to obtain activated apricot powder.

[0093] S3. Crosslinking treatment: The activated apricot powder obtained in step S2 and the asphalt are placed in a ball mill jar and ball-milled and mixed evenly, wherein the amount of asphalt added is 1.5% of the mass of the apricot powder, to obtain composite apricot powder.

[0094] S4. Oxidation treatment: The composite apricot powder obtained in step S3 is oxidized in an oxygen atmosphere at 200°C for 2 hours to obtain oxidized apricot powder.

[0095] S5. High-temperature carbonization: The oxidized apricot powder obtained in step S4 is heated to 800°C at 5°C / min under a nitrogen atmosphere, and then heated to 1200°C at 2°C / min and held for 4 hours to obtain the final hard carbon product material.

[0096] The electrochemical performance of the obtained materials was tested as follows: Hard carbon material, Super P, CMC, and SBR were mixed in a mass ratio of 94:1.5:2:2.5 to form a slurry. A 60 μm four-sided coating tool was used to coat the black slurry onto copper foil, and the membrane was then dried in a vacuum oven at 100°C for 2 hours. The electrode membrane was punched into 12 mm diameter discs using a die-cutting machine. Using metallic sodium as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) as the electrolyte, and a PP double-layer separator, CR2032 type button cells were assembled in a glove box. Constant current charge-discharge tests were performed on the above button cells at a current density of 0.1C (1C = 300 mAh / g) and a voltage range of 2–0.005 V.

[0097] Comparative Example 1

[0098] This embodiment relates to a biomass hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:

[0099] S1. Pretreatment: Preparation of biomass hard carbon materials: Crush bamboo raw materials and sieve them through a 60-mesh sieve to obtain bamboo powder raw materials.

[0100] S2. Activation treatment: Place the bamboo powder obtained by sieving in step S1 into a reaction vessel, add pure water, heat to 90°C, and react for 6 hours. Then, dry at 80°C for 12 hours to obtain the second bamboo powder.

[0101] S3. Crosslinking treatment: The second bamboo powder obtained in step S2 and phenolic resin are placed in a ball mill jar and ball-milled and mixed evenly, wherein the amount of phenolic resin added is 4% of the mass of bamboo powder, to obtain composite bamboo powder.

[0102] S4. Oxidation treatment: The composite bamboo powder obtained in step S3 is oxidized in an oxygen atmosphere at 220°C for 4 hours to obtain oxidized bamboo powder.

[0103] S5. High-temperature carbonization: The oxidized bamboo powder obtained in step S4 is heated to 800°C at 5°C / min under a nitrogen atmosphere, and then heated to 1300°C at 2°C / min and held for 2 hours to obtain the final hard carbon finished material.

[0104] The electrochemical performance of the obtained materials was tested as follows: Hard carbon material, Super P, CMC, and SBR were mixed in a mass ratio of 94:1.5:2:2.5 to form a slurry. A 60 μm four-sided coating tool was used to coat the black slurry onto copper foil, and the membrane was then dried in a vacuum oven at 100°C for 2 hours. The electrode membrane was punched into 12 mm diameter discs using a die-cutting machine. Using metallic sodium as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) as the electrolyte, and a PP double-layer separator, CR2032 type button cells were assembled in a glove box. Constant current charge-discharge tests were performed on the above button cells at a current density of 0.1C (1C = 300 mAh / g) and a voltage range of 2–0.005 V.

[0105] Comparative Example 2

[0106] This embodiment relates to a biomass hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:

[0107] S1. Pretreatment: Preparation of biomass hard carbon materials: Crush bamboo raw materials and sieve them through a 60-mesh sieve to obtain bamboo powder raw materials.

[0108] S2. Activation treatment: The bamboo powder obtained by sieving in step S1 is placed in a reaction vessel, a 1 mol / L sulfuric acid solution is added, and the mixture is heated to 90°C and reacted for 6 hours. Subsequently, it is dried at 80°C for 12 hours to obtain activated bamboo powder.

[0109] S3. Ball milling treatment: The activated bamboo powder obtained in step S2 is placed in a ball mill jar and ball milled to obtain the third bamboo powder.

[0110] S4. Oxidation treatment: The third bamboo powder obtained in step S3 is oxidized in an oxygen atmosphere at 220°C for 4 hours to obtain oxidized bamboo powder.

[0111] S5. High-temperature carbonization: The oxidized bamboo powder obtained in step S4 is heated to 800°C at 5°C / min under a nitrogen atmosphere, and then heated to 1300°C at 2°C / min and held for 2 hours to obtain the final hard carbon finished material.

[0112] The electrochemical performance of the obtained materials was tested as follows: Hard carbon material, Super P, CMC, and SBR were mixed in a mass ratio of 94:1.5:2:2.5 to form a slurry. A 60 μm four-sided coating tool was used to coat the black slurry onto copper foil, and the membrane was then dried in a vacuum oven at 100°C for 2 hours. The electrode membrane was punched into 12 mm diameter discs using a die-cutting machine. Using metallic sodium as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) as the electrolyte, and a PP double-layer separator, CR2032 type button cells were assembled in a glove box. Constant current charge-discharge tests were performed on the above button cells at a current density of 0.1C (1C = 300 mAh / g) and a voltage range of 2–0.005 V.

[0113] The above embodiments were subjected to relevant tests, and the test results are shown in Tables 1-2 and 2. Figure 1-4 As shown:

[0114] Table 1 Yield Test Results

[0115]

[0116] As shown in Table 1, the sample yield results indicate that the hard carbon materials in Application Examples 1 and 2 exhibit higher oxidation and total yields after acid activation before crosslinking with a crosslinking agent. In contrast, Comparative Example 1, which did not undergo acid activation before oxidation and was directly mixed with the crosslinking agent, showed lower oxidation and total yields. Furthermore, Comparative Example 2, which underwent acid activation before oxidation but did not undergo crosslinking with the crosslinking agent, also exhibited lower oxidation and total yields. This demonstrates that to prepare hard carbon materials with high oxidation and total yields, it is essential to acid activate the precursor before the oxidation process and introduce a crosslinking agent to complete the crosslinking reaction.

[0117] Table 2 Electrochemical performance test results

[0118]

[0119] From Table 2 and Figure 1-4The first-week charge-discharge curves showed that the hard carbon materials in Application Examples 1 and 2, after acid activation before oxidation and crosslinking with a crosslinking agent, exhibited high specific capacities of 346.30 mAh / g and 330.96 mAh / g, respectively, with corresponding first-week efficiencies of 92.95% and 91.91%. In contrast, Comparative Example 1, which was not acid-activated before oxidation and was directly mixed with the crosslinking agent, had a lower specific capacity of 298.42 mAh / g and a first-week efficiency of 92.69%. Comparative Example 2, which was acid-activated before oxidation but not crosslinked with the crosslinking agent, also had a lower specific capacity of 280.63 mAh / g and a first-week efficiency of 92.72%. These results indicate that to prepare hard carbon materials with high specific capacity, the precursor must be acid-activated before the oxidation process, and a crosslinking agent must be introduced to complete the crosslinking reaction.

[0120] The above embodiments are merely specific examples of the present invention, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.

Claims

1. A method for preparing high-yield biomass hard carbon anode material for sodium-ion batteries, characterized in that... Includes the following steps: S1. Pretreatment: The biomass raw material is crushed and sieved to obtain a refined precursor; S2. Activation treatment: The refined precursor obtained in step S1 is activated by an acidic solution and then dried to obtain the activated precursor. S3. Crosslinking treatment: The activated precursor obtained in step S2 is ball-milled and mixed with the crosslinking agent to obtain a composite precursor. S4. Oxidation treatment: The composite precursor obtained in step S3 is oxidized in an oxidizing atmosphere to obtain an oxidized precursor. S5. High-temperature carbonization: The oxide precursor obtained in step S4 is subjected to high-temperature carbonization to obtain the final hard carbon anode material.

2. The method for preparing high-yield sodium-ion battery biomass hard carbon anode material according to claim 1, characterized in that: In step S2, the acidic solution is one or more of the following: sulfuric acid, hydrochloric acid, nitric acid, boric acid, citric acid, oxalic acid, phytic acid, formic acid, propionic acid, acetic acid, and perchloric acid. The concentration of the acidic solution is 0.5-2 mol / L, the activation temperature is 80-120℃, and the activation time is 3-8 h.

3. The method for preparing high-yield sodium-ion battery biomass hard carbon anode material according to claim 1, characterized in that: In step S3, the crosslinking agent is one or more of asphalt, resin, and carbohydrate compounds.

4. The method for preparing high-yield sodium-ion battery biomass hard carbon anode material according to claim 1, characterized in that: In step S3, the amount of crosslinking agent added is 1-8% of the precursor mass.

5. The method for preparing high-yield sodium-ion battery biomass hard carbon anode material according to claim 1, characterized in that: In step S4, the oxidation temperature is 200-400℃, the oxidation time is 2-8h, and the oxidation atmosphere is air and / or ozone.

6. The method for preparing high-yield sodium-ion battery biomass hard carbon anode material according to claim 1, characterized in that: In step S5, the conditions for high-temperature carbonization are: heating rate of 1-5℃ / min, carbonization temperature of 1200-1600℃, and carbonization time of 2-10 h.

7. The method for preparing high-yield sodium-ion battery biomass hard carbon anode material according to claim 1, characterized in that: In step S1, the biomass raw materials are one or more of the following: walnut shells, chestnut shells, peanut shells, coconut shells, almond shells, camellia shells, corn cobs, sugarcane bagasse, wood chips, bamboo chips, corn stalks, wheat straw, rice straw, and cotton straw.

8. A biomass hard carbon anode material for sodium-ion batteries, characterized in that: It is prepared by any one of the preparation methods described in claims 1-7.

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