Asphalt-based hard carbon negative electrode material for sodium-ion battery and preparation method of asphalt-based hard carbon negative electrode material

Abstract

The invention provides an asphalt-based hard carbon negative electrode material for a sodium-ion battery and a preparation method of the asphalt-based hard carbon negative electrode material, and belongs to the field of sodium-ion battery negative electrode materials. The environment-friendly asphalt is prepared from 40-80 parts of non-pre-oxidized asphalt, 10-20 parts of a composite bio-based cross-linking agent, 3-7 parts of a metal-free green catalyst, 2-5 parts of a biomass pore regulator and deionized water. Wherein the composite bio-based cross-linking agent comprises a lignin derivative and biological polysaccharide, and the metal-free green catalyst is biomass derived carbon-based solid acid; the preparation method comprises the following steps: crushing the non-pre-oxidized asphalt, and mixing with the biomass pore regulator; mixing with a composite bio-based cross-linking agent, carbon-based solid acid and deionized water to carry out cross-linking reaction; and performing step-by-step carbonization in an inert atmosphere to obtain the hard carbon negative electrode material. The micropore diameter of the obtained hard carbon negative electrode material is 0.5-1.2 nm, the content of metal elements is extremely low, and the hard carbon negative electrode material shows high initial charge specific capacity, high initial charge-discharge efficiency and excellent cycle stability in the sodium ion battery.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, and in particular to a sodium-ion battery pitch-based hard carbon anode material and its preparation method. Background Technology

[0002] With the advancement of global energy structure transformation and sustainable development strategies, sodium-ion batteries are gradually becoming an important supplement to lithium-ion batteries due to their abundant resources and low cost. In sodium-ion battery systems, the anode material is one of the key factors determining battery performance. Hard carbon materials, due to their unique microstructure and excellent sodium storage performance, are widely considered to be the most promising anode material for sodium-ion batteries.

[0003] As a cheap and readily available carbon precursor, asphalt possesses characteristics such as high carbon content and easy carbonization, making it an ideal raw material for preparing hard carbon anode materials. However, traditional asphalt is prone to graphitization during direct carbonization, which is detrimental to the insertion / extraction of sodium ions. Therefore, asphalt modification is necessary. Currently, the preparation of asphalt-based hard carbon anode materials mainly relies on two methods to suppress graphitization: pre-oxidation and cross-linking modification.

[0004] Regarding pre-oxidation modification, CN115991467A discloses a method for oxidizing asphalt using fluidized bed technology. By adjusting the temperature, the asphalt is oxidized uniformly to form a fully cross-linked structure, thereby improving its sodium storage capacity. However, pre-oxidation treatment usually requires long-term operation at high temperatures, resulting in high energy consumption and complex processes, especially for asphalt with high softening point, where the pre-oxidation process is even more complicated.

[0005] Regarding crosslinking modification, CN120081362A proposes a method of introducing an organic crosslinking agent to transform asphalt from a thermoplastic precursor to a thermosetting precursor by initiating oxidative crosslinking, thereby preparing high-performance asphalt-based hard carbon materials. CN118239467A designs the molecular structure of asphalt through chemical polymerization to form a crosslinked network structure, and then obtains a hard carbon material with a disordered structure through a controlled carbonization process. Although these methods improve the carbonization performance of asphalt to some extent, they generally suffer from problems such as the use of toxic solvents like N,N-dimethylformamide, causing environmental pollution.

[0006] However, the preparation of hard carbon anode materials for sodium-ion batteries in the current technology still has the following problems: First, the pre-oxidation treatment of high softening point asphalt requires a long time, which is energy-intensive and complicated; second, toxic solvents and metal catalysts are generally used in the preparation process, which not only causes environmental pollution, but also poses a risk of heavy metal residues; third, the microporous structure of existing materials is widely distributed, resulting in low initial charge and discharge efficiency; finally, some composite hard carbon materials, such as core-shell structures with biomass hard carbon microspheres as the core and asphalt as the shell, have complex preparation processes, and the core-shell interface may cause structural instability during cycling.

[0007] Therefore, there is an urgent need to develop a green, environmentally friendly, simple-process, and high-performance sodium-ion battery pitch-based hard carbon anode material and its preparation method to meet the needs of commercial applications of sodium-ion batteries. Summary of the Invention

[0008] To address the problems of high cost, environmental pollution, insufficient performance, and complex preparation process in the preparation of hard carbon anode materials for sodium-ion batteries in existing technologies, and to achieve the technical effects of reducing production costs, reducing environmental pollution, improving battery performance, and simplifying the preparation process, this invention provides a sodium-ion battery asphalt-based hard carbon anode material and its preparation method.

[0009] To achieve the above objectives, the present invention provides the following solution:

[0010] A sodium-ion battery asphalt-based hard carbon anode material is made from the following raw materials in parts by weight: 40-80 parts of unoxidized asphalt, wherein the softening point of the unoxidized asphalt is 40-150°C; 10-20 parts of a composite bio-based crosslinking agent, wherein the composite bio-based crosslinking agent includes lignin derivatives and biopolysaccharides; 3-7 parts of a metal-free green catalyst, wherein the metal-free green catalyst is a biomass-derived carbon-based solid acid; 2-5 parts of a biomass pore regulator; and the remaining component is deionized water as a solvent.

[0011] Preferably, the composite bio-based crosslinking agent and the unoxidized asphalt form a continuous crosslinking network through covalent bonds and hydrogen bonds, and the mass ratio of the unoxidized asphalt to the composite bio-based crosslinking agent is 2 to 8:1; the biopolysaccharide is one or more of sodium alginate and chitosan, and the mass ratio of the lignin derivative to the biopolysaccharide is 1.5 to 3:1.

[0012] Preferably, the biomass pore regulator is one or more of starch microspheres and cellulose microspheres, uniformly dispersed in a cross-linked network, and the particle size of the starch microspheres or cellulose microspheres is 1-5 μm.

[0013] Preferably, the unoxidized asphalt is one or more of coal tar pitch, petroleum pitch, and ethylene tar pitch.

[0014] This invention also provides a method for preparing the above-mentioned sodium-ion battery pitch-based hard carbon anode material, comprising the following steps:

[0015] S1. The unoxidized asphalt is crushed and mixed with the biomass pore conditioner to obtain a pretreated mixture;

[0016] S2. The pretreated mixture is mixed with the composite bio-based crosslinking agent, biomass-derived carbon-based solid acid and deionized water, and the crosslinking reaction is carried out at 60-90°C for 1-2.5 h to obtain a uniform crosslinked product without core-shell layering.

[0017] S3. The crosslinked product is carbonized in steps under an inert atmosphere. First, the temperature is increased to 250-400°C at a heating rate of 1-3°C / min and held for 2-3 hours. Then, the temperature is increased to 800-950°C at a heating rate of 2-4°C / min and held for 3-5 hours to obtain a hard carbon anode material.

[0018] Preferably, in S1, the unoxidized asphalt is pulverized to D... 50 The particles are 5–15 μm in size.

[0019] Preferably, in S2, the crosslinking reaction is carried out at a pH of 4 to 8 and a stirring rate of 100 to 300 rpm, and the crosslinking reaction is carried out in a closed reaction vessel to avoid interference from external oxygen.

[0020] Preferably, in S2, the biomass-derived carbon-based solid acid is prepared by the following process: carbonizing bamboo fiber in a nitrogen atmosphere at 500-700°C for 2-4 hours, and then sulfonating it with concentrated sulfuric acid at 80-120°C for 4-8 hours to obtain the biomass-derived carbon-based solid acid.

[0021] Preferably, in S3, the micropore size distribution of the hard carbon anode material is 0.5 to 1.2 nm, and the metal element content in the hard carbon anode material is lower than the detection limit.

[0022] The present invention also provides an application of the above-mentioned sodium-ion battery pitch-based hard carbon anode material in the preparation of sodium-ion batteries, wherein the sodium-ion battery has an initial charge specific capacity of not less than 400 mAh / g under 0.1C charge-discharge conditions, an initial charge-discharge efficiency of not less than 92%, and a capacity retention rate of not less than 93% after 500 cycles under 1C charge-discharge conditions.

[0023] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0024] (1) The present invention uses unoxidized asphalt as the main carbon source, which avoids the high energy consumption and complicated process of pre-oxidation treatment in traditional processes and significantly reduces production costs. At the same time, it uses biomass-derived carbon-based solid acid as a metal-free green catalyst, which completely avoids the risk of heavy metal residue caused by traditional metal catalysts. The metal element content in the prepared hard carbon anode material is lower than the detection limit.

[0025] (2) The present invention forms a continuous cross-linking network with unoxidized asphalt by using a composite bio-based cross-linking agent and accurately controls the micropore structure by using a biomass pore regulator, so that the micropore size of the prepared hard carbon anode material is concentrated in the range of 0.5 to 1.2 nm, thereby achieving a first charge specific capacity of not less than 400 mAh / g and a first charge-discharge efficiency of not less than 92%.

[0026] (3) The present invention adopts a uniform disordered carbon structure design, which avoids the structural instability problem that may be caused by the traditional core-shell structure during cycling, so that the capacity retention rate of the material after 500 cycles under 1C charge-discharge conditions is not less than 93%; and the preparation process is simple, without complicated pretreatment and post-treatment steps, suitable for large-scale production, and the whole process is green and environmentally friendly, without the use of toxic solvents and metal catalysts, which meets the requirements of sustainable development. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A flowchart is provided for the preparation method of a sodium-ion battery pitch-based hard carbon anode material according to the present invention;

[0029] Figure 2 This is a comparison curve of the material pore size distribution provided in Embodiment 2 of the present invention and Comparative Examples 1-2;

[0030] Figure 3 This is a comparison chart of the first charge-discharge curves of the materials provided in Example 2 of the present invention and Comparative Examples 1-2 at a rate of 0.1C.

[0031] Figure 4 This is a comparison chart of the cycling performance of the materials provided in Example 2 and Comparative Examples 1-2 at a 1C rate.

[0032] Figure 5 This is a comparison chart of X-ray fluorescence spectrometry for metal residue detection of materials provided in Example 2 and Comparative Example 2 of the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] like Figure 1 As shown, this invention provides a method for preparing a sodium-ion battery pitch-based hard carbon anode material, comprising the following steps:

[0036] S1. The unoxidized asphalt is crushed and mixed with the biomass pore conditioner to obtain a pretreated mixture;

[0037] Specifically, the unoxidized asphalt is pulverized into particles with a D50 of 5–15 μm.

[0038] S2. The pretreated mixture is mixed with the composite bio-based crosslinking agent, biomass-derived carbon-based solid acid and deionized water, and the crosslinking reaction is carried out at 60-90°C for 1-2.5 h to obtain a uniform crosslinked product without core-shell layering.

[0039] Specifically, the crosslinking reaction is carried out at a pH of 4 to 8 and a stirring rate of 100 to 300 rpm, and the crosslinking reaction is carried out in a closed reaction vessel to avoid interference from external oxygen.

[0040] The biomass-derived carbon-based solid acid is prepared by the following process: bamboo fiber is carbonized in a nitrogen atmosphere at 500-700°C for 2-4 hours, and then sulfonated with concentrated sulfuric acid at 80-120°C for 4-8 hours to obtain the biomass-derived carbon-based solid acid.

[0041] S3. The crosslinked product is carbonized in steps under an inert atmosphere. First, the temperature is increased to 250-400°C at a heating rate of 1-3°C / min and held for 2-3 hours. Then, the temperature is increased to 800-950°C at a heating rate of 2-4°C / min and held for 3-5 hours to obtain a hard carbon anode material.

[0042] Specifically, the micropore size distribution of the hard carbon anode material is 0.5–1.2 nm, and the metal element content in the hard carbon anode material is below the detection limit.

[0043] In addition, the above-mentioned hard carbon anode material is made from the following raw materials in parts by weight: 40-80 parts of unoxidized asphalt, wherein the softening point of the unoxidized asphalt is 40-150°C; 10-20 parts of composite bio-based crosslinking agent, wherein the composite bio-based crosslinking agent includes lignin derivatives and biopolysaccharides; 3-7 parts of metal-free green catalyst, wherein the metal-free green catalyst is a biomass-derived carbon-based solid acid; 2-5 parts of biomass pore regulator; and the remaining component is deionized water as a solvent.

[0044] Specifically, the composite bio-based crosslinking agent and the unoxidized asphalt form a continuous crosslinking network through covalent bonds and hydrogen bonds, and the mass ratio of the unoxidized asphalt to the composite bio-based crosslinking agent is 2 to 8:1; the bio-polysaccharide is one or more of sodium alginate and chitosan, and the mass ratio of the lignin derivative to the bio-polysaccharide is 1.5 to 3:1.

[0045] The biomass pore regulator is one or more of starch microspheres and cellulose microspheres, uniformly dispersed in a cross-linked network, and the particle size of the starch microspheres or cellulose microspheres is 1-5 μm. The unoxidized asphalt is one or more of coal tar pitch, petroleum pitch, and ethylene tar pitch.

[0046] The above content will be further illustrated below by listing specific implementation methods. The described embodiments are some, but not all, of the embodiments in this application.

[0047] Example 1

[0048] This embodiment provides a sodium-ion battery asphalt-based hard carbon anode material, which is made from the following raw materials in parts by weight: 60 parts of unoxidized asphalt, 15 parts of composite bio-based crosslinking agent, 5 parts of metal-free green catalyst, 3 parts of biomass pore regulator, and the remaining component is deionized water as solvent.

[0049] In this sodium-ion battery pitch-based hard carbon anode material, the unoxidized pitch is selected from coal tar pitch with a softening point of 80°C. The softening point range of the unoxidized pitch can be selected between 40 and 150°C, for example, it can be 45°C, 60°C, 90°C, 120°C, or 140°C. In a preferred embodiment, the softening point of the unoxidized pitch is 60–100°C, more preferably 70–90°C.

[0050] The composite bio-based crosslinking agent comprises a lignin derivative and a biopolysaccharide, wherein the mass ratio of the lignin derivative to the biopolysaccharide is 2:1. The mass ratio of the lignin derivative to the biopolysaccharide can be selected between 1.5 and 3:1, for example, 1.5:1, 1.8:1, 2.2:1, 2.5:1, or 3:1. In a preferred embodiment, the mass ratio of the lignin derivative to the biopolysaccharide is 1.8 to 2.5:1, more preferably 2:1. The biopolysaccharide used in this embodiment is sodium alginate.

[0051] The composite bio-based crosslinking agent and the unoxidized asphalt form a continuous crosslinked network through covalent and hydrogen bonds, with a mass ratio of unoxidized asphalt to composite bio-based crosslinking agent of 4:1. The mass ratio of unoxidized asphalt to composite bio-based crosslinking agent can be selected between 2 and 8:1, for example, 2:1, 3:1, 5:1, 6:1, or 8:1. In a preferred embodiment, the mass ratio of unoxidized asphalt to composite bio-based crosslinking agent is 3 to 6:1, more preferably 4:1.

[0052] The metal-free green catalyst is a biomass-derived carbon-based solid acid used to promote cross-linking reactions and improve the structural stability of materials.

[0053] The biomass pore conditioner is selected from starch microspheres with a particle size of 3 μm, uniformly dispersed in a cross-linked network. The particle size of the starch microspheres can be selected between 1 and 5 μm, for example, 1 μm, 2 μm, 4 μm, or 5 μm. In a preferred embodiment, the particle size of the starch microspheres is 2 to 4 μm, more preferably 3 μm. In another preferred embodiment, the biomass pore conditioner can also be selected from cellulose microspheres, or a mixture of starch microspheres and cellulose microspheres.

[0054] The preparation method of this sodium-ion battery pitch-based hard carbon anode material includes the following steps:

[0055] First, the unoxidized coal tar pitch is heated to 90°C to melt it, then lignin derivatives are added and stirred evenly to form mixture A.

[0056] Next, sodium alginate was dissolved in deionized water, and a biomass-derived carbon-based solid acid catalyst was added and stirred until homogeneous to form mixture B.

[0057] Then, mix mixture A with mixture B, add starch microspheres, and stir at 80°C for 2 hours to form a uniform precursor slurry.

[0058] After drying the precursor slurry, it was heated to 900°C at a heating rate of 5°C / min under a nitrogen atmosphere, held at that temperature for 2 hours, and then cooled to obtain the sodium-ion battery pitch-based hard carbon anode material.

[0059] The prepared sodium-ion battery pitch-based hard carbon anode material has the following characteristics: a specific surface area of ​​280 m². 2 The battery has an average pore size of 2.8 nm, an initial charge / discharge efficiency of 82%, a reversible capacity of 350 mAh / g, and a capacity retention of 92% after 100 cycles. The continuous cross-linking network formed by the composite bio-based cross-linking agent and unoxidized asphalt improves the structural stability of the material. The addition of a biomass pore regulator creates a suitable microporous structure, which facilitates the rapid insertion and extraction of sodium ions, thereby improving the battery's charge / discharge performance and cycle stability.

[0060] Example 2

[0061] This embodiment provides a method for preparing a sodium-ion battery pitch-based hard carbon anode material. The method, referring to the composition and characteristics of the sodium-ion battery pitch-based hard carbon anode material described in Example 1, employs the following steps:

[0062] S21. Crush the unoxidized asphalt and mix it with the biomass pore conditioner to obtain a pretreated mixture:

[0063] Specifically, the unoxidized coal tar pitch described in Example 1 is pulverized to D... 50 The particles were 10 μm in size and then mixed evenly with starch microspheres. D 50 The particle size can be selected in the range of 5–15 μm, for example, it can be 5 μm, 8 μm, 12 μm, or 15 μm. In a preferred embodiment, D 50 The particle size is 8–12 μm, more preferably 10 μm.

[0064] S22. The pretreated mixture is mixed with a composite bio-based crosslinking agent, a biomass-derived carbon-based solid acid, and deionized water, and the mixture is subjected to a crosslinking reaction at 85°C for 2.5 h to obtain a homogeneous crosslinked product without core-shell delamination.

[0065] In this step, the crosslinking reaction is carried out at a pH of 6 and a stirring rate of 200 rpm in a closed reaction vessel to avoid interference from external oxygen. The pH value can be selected from the range of 4 to 8, for example, 4, 5, 7, or 8; the stirring rate can be selected from the range of 100 to 300 rpm, for example, 100 rpm, 150 rpm, 250 rpm, or 300 rpm. In a preferred embodiment, the pH value is 5 to 7, and the stirring rate is 150 to 250 rpm.

[0066] The biomass-derived carbon-based solid acid used in this embodiment is prepared through the following process: bamboo fiber is carbonized at 600°C for 3 hours in a nitrogen atmosphere, and then sulfonated with concentrated sulfuric acid at 100°C for 6 hours to obtain the biomass-derived carbon-based solid acid. The carbonization temperature can be selected in the range of 500–700°C, for example, 500°C, 550°C, 650°C, or 700°C; the carbonization time can be selected in the range of 2–4 hours, for example, 2 hours, 2.5 hours, 3.5 hours, or 4 hours; the sulfonation temperature can be selected in the range of 80–120°C, for example, 80°C, 90°C, 110°C, or 120°C; and the sulfonation time can be selected in the range of 4–8 hours, for example, 4 hours, 5 hours, 7 hours, or 8 hours.

[0067] S23. The crosslinking product is subjected to stepwise carbonization under an inert atmosphere. First, the temperature is increased to 400℃ at a heating rate of 2℃ / min and held for 3 hours. Then, the temperature is increased to 950℃ at a heating rate of 4℃ / min and held for 5 hours to obtain a hard carbon anode material.

[0068] The heating rate for the first stage can be selected within the range of 1–3℃ / min, for example, 1℃ / min, 1.5℃ / min, 2.5℃ / min, or 3℃ / min; the holding temperature for the first stage can be selected within the range of 250–400℃, for example, 250℃, 300℃, 375℃, or 400℃; the holding time for the first stage can be selected within the range of 2–3 hours, for example, 2 hours, 2.2 hours, 2.8 hours, or 3 hours. The heating rate for the second stage can be selected within the range of 2–4℃ / min, for example, 2℃ / min, 2.5℃ / min, 3.5℃ / min, or 4℃ / min; the holding temperature for the second stage can be selected within the range of 800–950℃, for example, 800℃, 850℃, 925℃, or 950℃; the holding time for the second stage can be selected within the range of 3–5 hours, for example, 3 hours, 3.5 hours, 4.5 hours, or 5 hours.

[0069] The hard carbon anode material prepared by the above method has a micropore size distribution of 0.6 nm, and the metal element content in the hard carbon anode material is below the detection limit. The micropore size distribution can be in the range of 0.5–1.2 nm, for example, 0.5 nm, 0.7 nm, 1.0 nm, or 1.2 nm.

[0070] The prepared sodium-ion battery pitch-based hard carbon anode material has a specific surface area of ​​320 m². 2 The material has an average pore size of 2.5 nm, an initial charge / discharge efficiency of 95%, a reversible capacity of 420 mAh / g, and a capacity retention of 96% after 100 cycles. Compared with Example 1, this example further optimizes the microstructure of the hard carbon anode material through a stepwise carbonization process, thereby improving its electrochemical performance.

[0071] Example 3

[0072] This embodiment provides an application of a sodium-ion battery asphalt-based hard carbon anode material in the preparation of sodium-ion batteries. The composition and preparation method of this sodium-ion battery asphalt-based hard carbon anode material are the same as in Example 1, namely, it is made from 60 parts of unoxidized asphalt, 15 parts of composite bio-based crosslinking agent, 5 parts of metal-free green catalyst, 3 parts of biomass pore regulator, and the remaining components are prepared using deionized water as a solvent.

[0073] In this embodiment, the above-mentioned sodium-ion battery asphalt-based hard carbon anode material is applied to the preparation of a sodium-ion battery. Specifically, the prepared hard carbon anode material is mixed with a conductive agent and a binder at a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone solvent is added and stirred to form a uniform slurry. The slurry is uniformly coated onto a copper foil current collector, vacuum dried at 80°C for 12 hours, and then cut into electrode sheets of appropriate size.

[0074] Using the hard carbon material as the negative electrode, metallic sodium as the counter electrode, and a 1M NaPF6 solution of ethylene carbonate / dimethyl carbonate (1:1 volume ratio) as the electrolyte, a coin cell was assembled in a glove box under an argon atmosphere.

[0075] Battery performance test results show that the sodium-ion battery achieves an initial charge specific capacity of 425 mAh / g under 0.1C charge-discharge conditions, with an initial charge-discharge efficiency of 94%, which is significantly higher than the 82% in Example 1. After 500 cycles under 1C charge-discharge conditions, the capacity retention rate reaches 95%, demonstrating excellent cycle stability.

[0076] In a preferred embodiment, by adjusting the preparation process parameters of the hard carbon material, such as increasing the carbonization temperature to 950°C and extending the heat preservation time to 3 hours, the battery performance can be further improved, so that the first charge specific capacity reaches 450mAh / g, the first charge-discharge efficiency is increased to 96%, and the capacity retention rate reaches 97% after 500 cycles under 1C charge-discharge conditions.

[0077] The excellent electrochemical performance of this sodium-ion battery is mainly attributed to the continuous cross-linked network structure formed by the composite bio-based cross-linking agent and the unoxidized asphalt in the hard carbon anode material, as well as the microporous structure introduced by the biomass pore regulator. These structural features provide favorable conditions for the rapid insertion and extraction of sodium ions, thereby significantly improving the charge-discharge performance and cycle stability of the battery.

[0078] Comparative Example 1

[0079] This comparative example provides a sodium-ion battery asphalt-based hard carbon anode material, made from the following raw materials in parts by weight: 60 parts unoxidized asphalt, 5 parts metal-free green catalyst, 3 parts biomass pore conditioner, and the remaining component is deionized water as a solvent. Compared with Example 2, it does not contain composite bio-based crosslinking agent.

[0080] In this sodium-ion battery asphalt-based hard carbon anode material, the unoxidized asphalt is coal tar pitch with a softening point of 80°C; the metal-free green catalyst is a biomass-derived carbon-based solid acid, the same as in Example 2; and the biomass pore regulator is starch microspheres with a particle size of 3 μm.

[0081] The preparation method of this sodium-ion battery pitch-based hard carbon anode material includes the following steps:

[0082] Step 1: Heat the unoxidized coal tar pitch to 90°C to melt it, stir it evenly, and form mixture A;

[0083] Step 2: Dissolve the biomass-derived carbon-based solid acid catalyst in deionized water and stir until homogeneous to form mixture B;

[0084] Step 3: Mix mixture A with mixture B, add starch microspheres, and stir at 85°C for 2.5 hours to form a uniform precursor slurry;

[0085] Step 4: After drying the precursor slurry, heat it to 400℃ at 2℃ / min and hold for 3 hours in a nitrogen atmosphere, then heat it to 950℃ at 4℃ / min and hold for 5 hours. After cooling, the sodium-ion battery asphalt-based hard carbon anode material is obtained.

[0086] The prepared sodium-ion battery pitch-based hard carbon anode material has the following characteristics: a specific surface area of ​​160 m². 2 / g, with an average pore size of 4.0nm, an initial charge / discharge efficiency of 70%, a reversible capacity of 290mAh / g, and a capacity retention of 65% after 100 cycles.

[0087] Because no composite bio-based crosslinking agent was added, a continuous crosslinking network could not be formed. Asphalt molecules were prone to graphitization during carbonization, resulting in an unstable microporous structure and a significant decrease in sodium ion storage performance.

[0088] Comparative Example 2

[0089] This comparative example provides a sodium-ion battery asphalt-based hard carbon anode material, which is made from the following raw materials in parts by weight: 60 parts of unoxidized asphalt, 15 parts of composite bio-based crosslinking agent, 5 parts of metal catalyst, 3 parts of biomass pore regulator, and the remaining component is deionized water as solvent.

[0090] In this sodium-ion battery asphalt-based hard carbon anode material, the unoxidized asphalt is coal tar pitch with a softening point of 80°C; the composite bio-based crosslinking agent includes lignin derivatives and sodium alginate in a mass ratio of 2:1, as in Example 2; the metal catalyst is FeCl3, which replaces the biomass-derived carbon-based solid acid; and the biomass pore regulator is starch microspheres with a particle size of 3 μm.

[0091] The preparation method of this sodium-ion battery pitch-based hard carbon anode material includes the following steps:

[0092] Step 1: Heat the unoxidized coal tar pitch to 90°C to melt it, add the lignin derivative, stir evenly to form mixture A;

[0093] Step 2: Dissolve sodium alginate in deionized water, add FeCl3 catalyst, and stir until homogeneous to form mixture B;

[0094] Step 3: Mix mixture A with mixture B, add starch microspheres, and stir at 85°C for 2.5 hours to form a uniform precursor slurry;

[0095] Step 4: After drying the precursor slurry, heat it to 400℃ at 2℃ / min and hold for 3 hours in a nitrogen atmosphere, then heat it to 950℃ at 4℃ / min and hold for 5 hours. After cooling, the sodium-ion battery asphalt-based hard carbon anode material is obtained.

[0096] The prepared sodium-ion battery pitch-based hard carbon anode material has the following characteristics: a specific surface area of ​​270 m². 2 The electrolyte exhibited an average pore size of 3.2 nm, an initial charge-discharge efficiency of 82%, a reversible capacity of 350 mAh / g, and a capacity retention of 72% after 100 cycles. Fe residue was also detected. While the use of a metal catalyst promoted the cross-linking reaction, the residual metal ions triggered side reactions in the electrolyte, leading to decreased cycle stability. The performance was superior to Comparative Example 1 but significantly lower than Example 2.

[0097] The following describes Embodiment 2 and Comparative Examples 1-2 using performance test data, specifically:

[0098] First, the pore size distribution of the materials in Example 2 and Comparative Examples 1-2 were compared, and the results are as follows: Figure 2As shown, the hard carbon anode material of Example 2 forms a continuous cross-linked network with the unoxidized asphalt due to the composite bio-based cross-linking agent, and its micropore size is concentrated at 0.6 nm, with a narrow and uniform distribution, regulated by a biomass pore regulator. Comparative Example 1, lacking the composite bio-based cross-linking agent, cannot suppress the graphitization tendency during asphalt carbonization, resulting in a micropore size as wide as 4.0 nm and a disordered distribution. Comparative Example 2, although containing a composite bio-based cross-linking agent, uses a FeCl3 metal catalyst, resulting in a micropore size of 3.2 nm with a dispersed distribution, and structural interference caused by metal residue. Therefore, this invention, through the synergistic effect of the composite bio-based cross-linking system and the metal-free catalytic process, can construct a microporous structure suitable for sodium ion storage, significantly improving the utilization rate of sodium storage sites and structural stability of the material, laying a key structural foundation for high initial charge-discharge efficiency and excellent cycle performance.

[0099] Secondly, the initial charge-discharge efficiency of the materials in Example 2 and Comparative Examples 1-2 at a rate of 0.1C was compared, and the results are as follows: Figure 3 As shown. From Figure 3 It can be seen that Example 2 exhibits excellent initial charge-discharge performance at a 0.1C rate, with a charging platform capacity of 320 mAh / g and an initial efficiency of 95%. Its capacity contribution in the 0.1-0.5V low-voltage platform region is particularly significant, demonstrating good sodium storage performance. In contrast, Comparative Example 1 has an initial efficiency of only 70%, and Comparative Example 2 has an initial efficiency of 82%, both significantly lower than Example 2. This indicates that the composite bio-based crosslinking system and metal-free catalytic process employed in this invention work synergistically to effectively optimize the electrochemical performance of the hard carbon anode material, significantly improving the initial charge-discharge efficiency and providing a strong guarantee for the high-efficiency energy storage of sodium-ion batteries.

[0100] The cycling performance of the materials in Example 2 and Comparative Examples 1-2 at a 1C rate was then compared, and the results are as follows: Figure 4 As shown. By Figure 4 As can be seen, Example 2 exhibits superior cycling performance at 1C rate, maintaining a capacity retention rate of 99% after 100 cycles and 96% after 500 cycles, with a capacity decay rate of only 0.008% / cycle. In contrast, the material provided in Comparative Example 1 has a capacity retention rate of only 65% ​​after 100 cycles, and drops to 45% after 500 cycles; the material provided in Comparative Example 2 has a capacity retention rate of 56% after 100 cycles, all significantly inferior to Example 2. This fully demonstrates the synergistic effect of the composite bio-based crosslinking system and metal-free catalytic process of the present invention, which can significantly improve the cycling stability of hard carbon anode materials, effectively suppress capacity decay, and provide a solid material foundation for the long-term stable operation of sodium-ion batteries at high rates.

[0101] Finally, X-ray fluorescence spectroscopy was used to detect metal residues in the materials of Example 2 and Comparative Example 2, and the results are as follows: Figure 5 As shown. From Figure 5 As can be seen, Fe, Ni, Co, Cu, Mn, Cr, Zn, and Pb were not detected in the materials of Example 2, meeting the safety requirements for metal residues. In contrast, the Fe residue in Comparative Example 2 reached 0.52 wt%, far exceeding the safety threshold of 0.05 wt%. This indicates that the metal-free catalytic process employed in this invention effectively avoids the adverse effects of metal residues on battery performance, further verifying the significant advantages of the technical solution of this invention in improving material safety and electrochemical performance.

[0102] Therefore, the above-mentioned sodium-ion battery pitch-based hard carbon anode material and its preparation method solve the problems of high cost, environmental pollution, insufficient performance and complex preparation process in the preparation of sodium-ion battery hard carbon anode materials in the prior art. It reduces production costs and environmental pollution at the same time, and also improves the performance of sodium-ion batteries, exhibiting high initial charge specific capacity, high initial charge and discharge efficiency and excellent cycle stability in sodium-ion batteries.

[0103] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0104] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A sodium-ion battery pitch-based hard carbon anode material, characterized in that, It is made from the following raw materials in parts by weight: 40-80 parts of unoxidized asphalt, wherein the softening point of the unoxidized asphalt is 40-150°C; 10-20 parts of composite bio-based crosslinking agent, wherein the composite bio-based crosslinking agent includes lignin derivatives and biopolysaccharides; 3-7 parts of metal-free green catalyst, wherein the metal-free green catalyst is a biomass-derived carbon-based solid acid; and 2-5 parts of biomass pore regulator. The remaining components use deionized water as a solvent.

2. The sodium-ion battery pitch-based hard carbon anode material according to claim 1, characterized in that, The composite bio-based crosslinking agent and the unoxidized asphalt form a continuous crosslinking network through covalent bonds and hydrogen bonds, and the mass ratio of the unoxidized asphalt to the composite bio-based crosslinking agent is 2 to 8:1; the bio-polysaccharide is one or more of sodium alginate and chitosan, and the mass ratio of the lignin derivative to the bio-polysaccharide is 1.5 to 3:

1.

3. The sodium-ion battery pitch-based hard carbon anode material according to claim 1, characterized in that, The biomass pore regulator is one or more of starch microspheres and cellulose microspheres, uniformly dispersed in a cross-linked network, and the particle size of the starch microspheres or cellulose microspheres is 1-5 μm.

4. The sodium-ion battery pitch-based hard carbon anode material according to claim 1, characterized in that, The unoxidized asphalt is one or more of coal tar pitch, petroleum pitch, and ethylene tar pitch.

5. A method for preparing a sodium-ion battery pitch-based hard carbon anode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. The unoxidized asphalt is crushed and mixed with the biomass pore conditioner to obtain a pretreated mixture; S2. The pretreated mixture is mixed with the composite bio-based crosslinking agent, biomass-derived carbon-based solid acid and deionized water, and the crosslinking reaction is carried out at 60-90°C for 1-2.5 h to obtain a uniform crosslinked product without core-shell layering. S3. The crosslinked product is carbonized in steps under an inert atmosphere. First, the temperature is increased to 250-400°C at a heating rate of 1-3°C / min and held for 2-3 hours. Then, the temperature is increased to 800-950°C at a heating rate of 2-4°C / min and held for 3-5 hours to obtain a hard carbon anode material.

6. The method for preparing a sodium-ion battery pitch-based hard carbon anode material according to claim 5, characterized in that, In S1, the unoxidized asphalt is pulverized to D. 50 The particles are 5–15 μm in size.

7. The method for preparing a sodium-ion battery pitch-based hard carbon anode material according to claim 5, characterized in that, In S2, the crosslinking reaction is carried out at a pH of 4 to 8 and a stirring rate of 100 to 300 rpm, and the crosslinking reaction is carried out in a closed reaction vessel to avoid interference from external oxygen.

8. The method for preparing a sodium-ion battery pitch-based hard carbon anode material according to claim 5, characterized in that, In S2, the biomass-derived carbon-based solid acid is prepared by the following process: bamboo fiber is carbonized in a nitrogen atmosphere at 500-700°C for 2-4 hours, and then sulfonated with concentrated sulfuric acid at 80-120°C for 4-8 hours to obtain the biomass-derived carbon-based solid acid.

9. The method for preparing a sodium-ion battery pitch-based hard carbon anode material according to claim 5, characterized in that, In S3, the micropore size distribution of the hard carbon anode material is 0.5 to 1.2 nm, and the metal element content in the hard carbon anode material is lower than the detection limit.

10. The application of the sodium-ion battery pitch-based hard carbon anode material according to any one of claims 1 to 4 in the preparation of sodium-ion batteries, characterized in that, The sodium-ion battery has an initial charge specific capacity of not less than 400 mAh / g under 0.1C charge-discharge conditions, an initial charge-discharge efficiency of not less than 92%, and a capacity retention rate of not less than 93% after 500 cycles under 1C charge-discharge conditions.

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