A surface-chemically reconstructed sodium-ion battery hard carbon negative electrode material and a preparation method thereof

Abstract

The application discloses a kind of surface chemical reconfiguration's sodium ion battery hard carbon negative electrode material and preparation method thereof.The method comprises the following steps: constructing organic precursor layer on the surface of carbon source matrix;Using acid dehydrating agent to induce the dehydration, crosslinking or aromatization reaction of precursor layer at 0-300 DEG C, to form stable surface solidification layer;Finally, high-temperature carbonization is obtained hard carbon material.The application utilizes acid-assisted solidification technology, significantly reduces the content of active oxygen-containing functional groups on the surface of hard carbon (XPS shows <5.0%), while maintaining the internal microporous sodium storage capacity, significantly improves the interface stability and the first coulomb efficiency of the material (can reach more than 95%).The process is simple, low in cost, and suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials technology, specifically relating to a surface chemically reconstructed hard carbon anode material for sodium-ion batteries and its preparation method. Background Technology

[0002] Sodium-ion batteries are considered a strong contender for next-generation large-scale energy storage technology due to their abundant resources and low cost. Among various anode materials, hard carbon is the preferred choice for commercialization due to its structural stability and high sodium storage capacity. However, hard carbon materials face a significant bottleneck: low initial coulombic efficiency (ICE). Typically, unmodified hard carbon has an ICE of only 70%–85%. A low ICE means that during the first charge of the battery, a large amount of active sodium ions from the cathode are irreversibly consumed, forming a solid electrolyte interphase (SEI) film or being trapped by surface defects. To compensate for this loss, it is often necessary to use excessive cathode material or employ complex pre-sodiumification techniques, which not only increases battery cost but also reduces overall energy density.

[0003] Existing methods for improving ICE (Internal Capacity Expansion) mainly include surface CVD carbon coating, surface fluorination, and alumina coating. However, CVD processes are expensive and use hazardous gases; inorganic coatings often have poor conductivity, affecting rate performance. Furthermore, it is generally believed in the industry that the larger the specific surface area of ​​hard carbon, the more side reactions occur, and the lower the ICE. Therefore, existing modification approaches mostly focus on simply reducing the specific surface area, but this often comes at the cost of sacrificing the microporous sodium storage capacity of hard carbon, leading to a decrease in reversible capacity.

[0004] Therefore, developing a hard carbon preparation technology for ICE that is simple, low-cost, and can significantly improve ICE capacity while maintaining high capacity is an urgent need in the industry. Summary of the Invention

[0005] This invention aims to solve the technical problems of low initial efficiency and large irreversible capacity of existing hard carbon anode materials, and provides a high initial efficiency hard carbon preparation method based on acid-assisted surface modification.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a surface chemically reconstructed hard carbon anode material for sodium-ion batteries includes the following steps:

[0008] (1) Construction of interfacial organic precursor: A layer of acid-curable organic precursor component is constructed or introduced on the surface of carbon source matrix to obtain composite precursor;

[0009] (2) Acid-induced curing and reconstruction: The composite precursor is contacted with an acidic dehydrating agent and chemical curing reaction is carried out in the temperature range of 0℃ to 300℃ to induce the organic precursor components to undergo chemical reactions including dehydration, crosslinking, condensation, aromatization or elimination of surface active groups to form a structurally stable surface curing layer or a densified structure.

[0010] (3) High-temperature carbonization treatment: Depending on the curing process, the cured product can be cleaned to remove residual acid before carbonization or carbonized directly. The carbonization is carried out in a non-oxidizing atmosphere at a high temperature of 1000℃ to 1600℃ to obtain the hard carbon anode material.

[0011] In addition, in step (2), the chemical curing reaction is not limited to heating with an external heat source, but also includes curing by using the exothermic reaction (self-heating) generated when an acidic dehydrating agent (such as concentrated sulfuric acid) comes into contact with organic components, or by extending the curing time at room temperature.

[0012] The beneficial effects of this invention are as follows:

[0013] 1. Significantly Improved Initial Coulombic Efficiency: The hard carbon material prepared by this invention exhibits extremely high chemical inertness and density. Without pre-sodiumization with metallic sodium, this material demonstrates extremely high interfacial stability in sodium-ion battery tests, with an initial coulombic efficiency consistently above 95%.

[0014] 2. Surface chemical inertization: XPS characterization confirmed that after treatment by the method of the present invention, chemical reactions, including dehydration, crosslinking, condensation, aromatization or elimination of surface active groups, occur on the surface of the material, forming a surface-cured layer or a densified structure that is physically stable and chemically inert.

[0015] 3. High capacity retention: While achieving surface densification and reconstruction, this method fully preserves the microporous sodium storage structure inside the hard carbon, and the reversible specific capacity of the material is maintained above 300 mAh / g, achieving both high initial efficiency and high capacity.

[0016] 4. Strong process versatility: This method has significant effects on a variety of carbon source precursors and a variety of acidic media (such as sulfuric acid and organic sulfonic acid), and breaks the absolute dependence on external heat field. The process equipment is simple and easy to scale up industrially. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0018] A method for preparing a surface chemically reconstructed hard carbon anode material for sodium-ion batteries includes the following steps:

[0019] (1) Construction of interfacial organic precursor: Provide a carbon source matrix and construct or introduce an acid-curable organic precursor component on its surface to obtain a composite precursor;

[0020] (2) Acid-induced curing and reconstruction: The composite precursor is contacted with an acidic dehydrating agent and chemical curing reaction is carried out in the temperature range of 0℃ to 300℃. The organic precursor components are induced to undergo chemical reactions including dehydration, crosslinking, condensation, aromatization or elimination of surface active groups to form a structurally stable surface curing layer or a densified structure, and the cured product is obtained.

[0021] (3) Post-treatment and carbonization: The solidified product is subjected to high-temperature carbonization after removing residual free acid, or the high-temperature carbonization is carried out directly when the acidic dehydrating agent is solid or the in-situ reaction is completely consumed; the high-temperature carbonization is carried out in a non-oxidizing atmosphere at 1000°C to 1600°C, and the hard carbon anode material is obtained after cooling.

[0022] The carbon source matrix in step (1) is selected from carbonized hard carbon materials, soft carbon materials, graphite, mesophase carbon microspheres or their precursors; the construction method of the interfacial organic precursor is selected from any of the following:

[0023] (a) Surface coating method: coating an organic polymer layer by in-situ polymerization, liquid phase coating or mechanical fusion;

[0024] (b) Blending modification method: The carbon source matrix or its precursor is mixed with organic precursor components and acidic dehydrating agent;

[0025] (c) In-situ growth method: A biomass or organic molecular membrane is grown or adsorbed in situ on the surface of a carbon source substrate.

[0026] The organic precursor component is selected from one or more of the following groups:

[0027] (a) Nitrogen- or oxygen-containing heterocyclic polymers, including polydopamine, polypyrrole, polyaniline, and polyimide;

[0028] (b) Synthetic resins, including phenolic resins, epoxy resins, and furan resins;

[0029] (c) Biomass and its derivatives, including glucose, sucrose, starch, cellulose, and lignin;

[0030] (d) Petroleum or coal tar pitch.

[0031] The acidic dehydrating agent mentioned in step (2) is selected from one or more of the following groups:

[0032] (a) Liquid inorganic strong acids, including concentrated sulfuric acid, fuming sulfuric acid, polyphosphoric acid, and nitric acid;

[0033] (b) Organic sulfonic acid compounds, including p-benzenesulfonic acid, methanesulfonic acid, and dodecylbenzenesulfonic acid;

[0034] (c) Solid acids or Lewis salts, including sodium bisulfate, potassium bisulfate, zinc chloride, aluminum chloride, and boric acid;

[0035] The acidic dehydrating agent is introduced by liquid phase impregnation, spray mixing, in-situ concentration, or gas phase fumigation.

[0036] The chemical curing reaction process described in step (2) satisfies one of the following conditions:

[0037] (a) Using an external heat source, the reaction temperature is controlled between 50°C and 300°C, and the reaction time is between 0.5 hours and 24 hours;

[0038] (b) Self-heating curing is carried out by utilizing the exothermic reaction generated by the contact between the acidic dehydrating agent and the precursor, with a reaction time of 0.5 hours to 24 hours;

[0039] (c) Allow the reaction to stand at room temperature (0℃-40℃) for 0.5 hours to 24 hours.

[0040] In the high-temperature carbonization process described in step (3), the non-oxidizing atmosphere is nitrogen, argon, helium, and other gases that do not react with carbon; the high-temperature carbonization holding time is 1 to 10 hours.

[0041] A hard carbon anode material prepared by the aforementioned method comprises an internal porous carbon framework and a surface acid-modified dense layer. The acid-modified dense layer is an amorphous carbon layer formed by carbonization of an in-situ acid-cured organic layer, and possesses the following physicochemical properties:

[0042] (a) Surface passivation characteristics: X-ray photoelectron spectroscopy (XPS) tests showed that the peak area of ​​the active oxygen-containing functional groups (binding energy range of 286.5-289.0 eV) in the C1s spectrum of the material surface accounted for less than 5.0% of the total carbon peak area;

[0043] (b) Structural characteristics: Nitrogen adsorption-desorption test (BET) showed that the specific surface area of ​​the material was 10-60 m² / g.

[0044] A sodium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the negative electrode comprises the hard carbon negative electrode material of claim 7.

[0045] The electrolyte contains an organic solvent and a sodium salt, wherein the organic solvent is selected from one or more of ether solvents, ester solvents, sulfone solvents, or ionic liquids.

[0046] Example 1

[0047] This embodiment provides a method for preparing hard carbon based on polydopamine (PDA)-assisted acid modification.

[0048] (1) Interface layer construction: 5g of commercial hard carbon powder was dispersed in Tris buffer (pH=8.5), 1g of dopamine hydrochloride was added, and the mixture was stirred for 6 hours to allow dopamine to polymerize in situ on the surface of hard carbon to form a PDA coating layer. The mixture was then centrifuged and dried.

[0049] (2) Acid-induced curing: The hard carbon powder coated with PDA was immersed in 200 mL of concentrated sulfuric acid (98%). The reaction heat and dehydration properties generated instantaneously upon contact between concentrated sulfuric acid and PDA were utilized. The reaction was mainly exothermic, and external heating was used as needed to maintain the reaction temperature at approximately 100°C for 4 hours. During this process, concentrated sulfuric acid induced deep dehydration, cross-linking, and elimination of surface active groups in the PDA layer, forming a dense cured layer.

[0050] (3) Cleaning and carbonization: The slurry after reaction is poured into deionized water for quenching, filtered and washed until neutral, and dried. Then it is placed in a tube furnace and calcined at 1100℃ for 2 hours under an argon atmosphere.

[0051] (4) Performance testing: A coin cell was assembled using the prepared material as the working electrode, metallic sodium as the counter electrode, and 1.0 M NaPF6 in DME as the electrolyte. The test results showed that the material had a first charge specific capacity of 310.5 mAh / g, a first discharge specific capacity of 304.6 mAh / g, and a first coulombic efficiency as high as 98.1%.

[0052] Example 2

[0053] This embodiment provides a method for preparing hard carbon based on organic solid acid modification.

[0054] (1) Mixing: 5g of commercial hard carbon and 1g of glucose were ball-milled and mixed, and then 0.5g of p-benzenesulfonic acid (PTSA) powder was added and mechanically mixed and ground.

[0055] (2) Curing: The mixed powder is heat-treated at 200°C for 3 hours to induce PTSA melting and chemically modify and cure the hard carbon surface.

[0056] (3) Carbonization: Carbonize at 1100℃ in an argon atmosphere for 2 hours.

[0057] (4) Performance test: The test results show that the ICE of the modified material is increased to 92.5% compared with the untreated commercial hard carbon (ICE=82%).

[0058] Comparative Example 1

[0059] Hard carbon that has only undergone PDA coating but not concentrated sulfuric acid chemical curing is directly carbonized.

[0060] Result: ICE was 88.5%.

[0061] Comparative Example 2

[0062] Commercial hard carbon without PDA coating is directly treated with concentrated sulfuric acid.

[0063] Result: ICE was 86.3%.

[0064] To further verify the influence of the preparation method described in this invention on the microstructure and electrochemical performance of the material, the inventors conducted systematic physicochemical parameter tests on the samples prepared in Examples 1 and 2, as well as Comparative Examples 1 and 2. The test results are summarized in Table 1.

[0065] Sample number Surface modification treatment methods BET specific surface area (m² / g) XPS C1s spectrum: percentage of active oxygen-containing functional groups (%) First charge specific capacity (mAh / g) Initial discharge specific capacity (mAh / g) First Coulomb Efficiency (ICE, %) Example 1 PDA coating + concentrated sulfuric acid curing 52 1.2 310.5 304.6 98.1 Example 2 Glucose / PTSA + self-heating curing 15.4 3.8 305.2 282.3 92.5 Comparative Example 1 PDA coating only (acid-free curing) 70.5 8.4 308.1 272.6 88.5 Comparative Example 2 Treatment with concentrated sulfuric acid only (no precursor) 10.3 6.5 295.4 254.9 86.3 Reference Sample Raw, untreated hard carbon 6 11.2 290 237.8 82

[0066] The percentage of active oxygen-containing functional groups refers to the percentage of the sum of the peak areas of CO, C=O, and OC=O with binding energies in the 286.5-289.0 eV range in the high-resolution C1s spectrum of X-ray photoelectron spectroscopy (XPS) to the total carbon peak area.

[0067] It should be noted that in this invention, "acid-induced curing" refers to a series of complex chemical reactions that occur in the precursor under the action of an acidic medium. Regardless of whether an external thermal field is applied to the process, and regardless of whether the process is described as dehydration, condensation, crosslinking, aromatization, or as the removal, cleaning, or passivation of surface functional groups, as long as it utilizes the chemical potential energy of the acidic medium to achieve the stabilization or densification of the precursor surface, it falls within the protection scope of this invention.

Claims

1. A method for preparing a surface chemically reconstructed hard carbon anode material for sodium-ion batteries, characterized in that, Includes the following steps: (1) Construction of interfacial organic precursor: Provide a carbon source matrix and construct or introduce an acid-curable organic precursor component on its surface to obtain a composite precursor; (2) Acid-induced curing and reconstruction: The composite precursor is contacted with an acidic dehydrating agent and chemical curing reaction is carried out in the temperature range of 0℃ to 300℃. The organic precursor components are induced to undergo chemical reactions including dehydration, crosslinking, condensation, aromatization or elimination of surface active groups to form a structurally stable surface curing layer or a densified structure, and the cured product is obtained. (3) High-temperature carbonization treatment: Depending on the curing process, the cured product can be cleaned to remove residual acid before carbonization or carbonized directly. The carbonization is carried out in a non-oxidizing atmosphere at a high temperature of 1000°C to 1600°C, and the hard carbon anode material is obtained after cooling.

2. The preparation method according to claim 1, characterized in that, The carbon source matrix in step (1) is selected from carbonized hard carbon materials, soft carbon materials, graphite, mesophase carbon microspheres or their precursors; the construction method of the interfacial organic precursor is selected from any of the following: (a) Surface coating method: coating an organic polymer layer by in-situ polymerization, liquid phase coating or mechanical fusion; (b) Blending modification method: The carbon source matrix or its precursor is mixed with organic precursor components and acidic dehydrating agent; (c) In-situ growth method: A biomass or organic molecular membrane is grown or adsorbed in situ on the surface of a carbon source substrate.

3. The preparation method according to claim 1, characterized in that, The organic precursor component is selected from one or more of the following groups: (a) Nitrogen- or oxygen-containing heterocyclic polymers, including polydopamine, polypyrrole, polyaniline, and polyimide; (b) Synthetic resins, including phenolic resins, epoxy resins, and furan resins; (c) Biomass and its derivatives, including glucose, sucrose, starch, cellulose, and lignin; (d) Petroleum or coal tar pitch.

4. The preparation method according to claim 1, characterized in that, The acidic dehydrating agent mentioned in step (2) is selected from one or more of the following groups: (a) Liquid inorganic strong acids, including concentrated sulfuric acid, fuming sulfuric acid, polyphosphoric acid, and nitric acid; (b) Organic sulfonic acid compounds, including p-benzenesulfonic acid, methanesulfonic acid, and dodecylbenzenesulfonic acid; (c) Solid acids or Lewis salts, including sodium bisulfate, potassium bisulfate, zinc chloride, aluminum chloride, and boric acid; The acidic dehydrating agent is introduced by liquid phase impregnation, spray mixing, in-situ concentration, or gas phase fumigation.

5. The preparation method according to claim 1, characterized in that, The chemical curing reaction process described in step (2) satisfies one of the following conditions: (a) Using an external heat source, the reaction temperature is controlled between 50°C and 300°C, and the reaction time is between 0.5 hours and 24 hours; (b) Self-heating curing is carried out by utilizing the exothermic reaction generated by the contact between the acidic dehydrating agent and the precursor, with a reaction time of 0.5 hours to 24 hours; (c) Allow the reaction to stand at room temperature (0℃-40℃) for 0.5 hours to 24 hours.

6. The preparation method according to claim 1, characterized in that, In the high-temperature carbonization process described in step (3), the non-oxidizing atmosphere is nitrogen, argon, helium, and other gases that do not react with carbon; the high-temperature carbonization holding time is 1 to 10 hours.

7. A hard carbon anode material prepared by the method according to any one of claims 1-6, characterized in that, The material consists of an internal porous carbon skeleton and an acid-modified dense layer on the surface. The acid-modified dense layer is an amorphous carbon layer formed by carbonization of an in-situ acid-cured organic layer.

8. A sodium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the negative electrode comprises the hard carbon negative electrode material as described in claim 7.

9. The sodium-ion battery according to claim 8, characterized in that, The electrolyte contains an organic solvent and a sodium salt, wherein the organic solvent is selected from one or more of ether solvents, ester solvents, sulfone solvents, or ionic liquids.